Fig. 247.
Fig.247.—Tillotherium fodiens.Left lateral view of skull. (From Flower, after Marsh.)
These animals have been regarded as ancestral Rodents, to which the tooth characters just mentioned clearly show likenesses. The earliest known form isEsthonyx. This genus shows such primitive characters, compared with its later representatives, as the existence of all three pairs of incisors in the upper jaw, but only two in the lower jaw. The enlarged incisors of both jaws do not seem to have grown from persistent pulps.
Anchippodus, a later form, still preserves the upper pair of first incisors in a vestigial form; the strong second incisors grew from persistent pulps. The most recent genus,Tillotherium, shows the characteristics of the group at their height. The strong Rodent-like, chisel-shaped incisors, which are reinforced by a small additional pair in the upper jaws only, are persistent. The grinding teeth are of the tritubercular pattern; there are three of each kind in the upper jaw, but in the lower jaw only two premolars on each side. This is at any rate the case with some, while others have three. The canine, though present in both jaws, is insignificant. As in many ancient types, there is an entepicondylar foramen in the humerus. The feet were five-toed, and bore sharp, laterally-compressed claws. The skull has been compared in general aspect to that of a Bear.
The Insectivora[365]are an order of mammals to which it is (to quote Professor Huxley) "exceedingly difficult to give a definition." They are, however, none of them large animals, and most of them are nocturnal in habit—two circumstances which may have had something to do with their survival from past ages, as may have also their modification to so many and diverse modes of life; for everything points to the antiquity of the group. They are, for instance, more or less plantigrade. The snout is generally long, and is often prolonged into a short proboscis.[366]There is a tendency for the teeth to be of a generalised type, and their number is often the typical mammalian forty-four. Moreover, trituberculate teeth, which are certainly an ancient form of tooth, are common; and indeed the Insectivora of the southern regions of the globe,e.g.Centetidae, Solenodontidae, and Chrysochloridae, have the most prevalent trituberculism, a fact which is of importance in considering the age of the animal life of these regions of the world. The limbs are, as a rule, provided with five digits. The hemispheres of the brain are usually smooth, and do not extend over the cerebellum. The palate is often fenestrate as in the Marsupials, and as in that group the lower jaw is sometimes inflected. But the latter character also occurs in the Sea-lions and elsewhere. Clavicles are present, as a rule, but not inPotamogale.
There is, furthermore, a distinct tendency towards a disappearance of functional milk teeth, which is best seen inSorex, where there are only seven milk teeth, none of which ever cut the gum. This suppression of the milk dentition is like that of the Marsupials, Edentates, and Whales, all of which appear to be—the first certainly are—ancient forms of mammalian life.
There is also a fairly well-defined, though shallow, cloaca in many genera. Finally, the testes are purely abdominal in some, and in none is there a full descent into a scrotum, as in the more highly-developed Eutheria.
Fam. 1. Erinaceidae.—This family contains the generaErinaceus,Hylomys, andGymnura.
Hylomys, considered by Dobson to fall withinGymnura, is kept separate by Leche.[367]H. suillusis a Malayan animal, small in size, about 5 inches long, with a short tail. LikeGymnurait is spineless. The ears are decidedly large and nude. There is one pair of inguinal and one pair of thoracic teats. The colour above is a rusty brown with yellowish-white under parts. The palms and soles are quite naked. In its general form it recallsTupaiavery much more than its own immediate relatives. There is no doubt, however, of its systematic position when the skeleton and teeth are examined. A variety has been described from altitudes of 3000 to 8000 feet on Mount Kina Balu in Borneo. It has the complete dentition of forty-four teeth. There are fourteen pairs of ribs. As inGymnurathe tibia and fibula are united below. The genus is considered by Leche to be the oldest existing type of Erinaceidae.
Gymnura[368]is also a Malayan form with the complete dentition of the last, but with fifteen pairs of ribs and a longer tail, consisting of twenty-three vertebrae as against fourteen. There is, as withHylomys, but one species,G. rafflesii. This animal has a peculiar odour, resembling decomposed cooked vegetables.The under surface of the tail is rough, and it is thought by Dr. Blanford that it may be of use to the animal in climbing. Its compressed terminal third and the fringe of stiff bristles on the under surface of this indicate, according to Dr. Dobson, powers of swimming, or at any rate a not very remote ancestry of swimming creatures. It is purely insectivorous in diet.
Erinaceus, including the Hedgehogs, is a widely distributed genus—Palaearctic, Oriental, and Ethiopian in range. There are about twenty species. The familiar spines distinguish the Hedgehogs from their allies, as also the fact that they possess but thirty-six teeth, the formula being I 3/2 C 1/1 Pm 3/2 M 3/3. There are fifteen or fourteen ribs, and the tail is very short, consisting of only twelve vertebrae. As inGymnurathere is no caecum. The upper canine has usually, as in other Erinaceidae, two roots, but not inE. europaeus, which is one of the most modified of Hedgehogs.
The Hedgehog is a more omnivorous creature thanGymnura. It eats not only insects and slugs, but also chickens and young game birds, and lastly vipers. Four, or in some cases as many as five or six, young are produced at a birth; they are blind, with soft and flexible white spines. In hot and dry weather Hedgehogs disappear; they come forth in rainy weather. The English Hedgehog, as is well known, hibernates. The Indian species do not. The Hedgehog is occasionally spineless, which condition may be regarded as an atavistic reversion.[369]
The Hedgehog has acquired the reputation of carrying off apples transfixed upon its spines. Blumenbach thus quaintly describes this and other habits of the animal, whose English name he gives as "hedgidog": "Il se nourrit des productions des deux règnes organisés, miaule comme un chat, et peut avaler une quantité énorme de mouches cantharides. Il est certain qu'il pique les fruits avec les épines de son dos, et les porte ainsi dans son terrier."[370]
The MiocenePalaeoerinaceusis so little different fromErinaceusthat it is really hardly generically separable.Erinaceusis therefore clearly one of the oldest living genera of mammals.
Necrogymnuraof the same epoch and the same beds (Quercy Phosphorites) is doubtless an ancestral form. The palate isperforated as inErinaceus(it is not so inGymnuraandHylomys), but on the whole it comes nearest toHylomys.
Fam. 2. Tupaiidae.—This family contains the generaTupaiaandPtilocercus.Tupaiais Oriental in range, extending as far east as Borneo. There are a dozen or so of species, which are generally arboreal and have the outward aspect of Squirrels. It has been suggested that this is a case of mimicry, the animal gaining some advantage by its likeness to the Rodent. The name Tupaia, it should be added, means Squirrel, and the long-nosed Squirrel,Sciurus laticaudatus, is so extraordinarily like it that "one has to look at the teeth" to distinguish them. Moreover this Squirrel, like some Tupaias, lives largely on the ground among fallen logs.Tupaiaresembles a Lemur in the complete orbit. The dental formula is I 2/3 C 1/1 Pm 3/3 M 3/3 = 38. The sublingua, too, is stated by Garrod to be like that ofChiromys. There is a minute caecum inT. belangeri, none inT. tana.
Ptilocercus[371]has a pen-like posterior portion to the tail, a modification which is found in other groups of animals. The tail of certain Phalangers, for instance, shows this same modification. The rest of the tail is scaly. The animal, as was pointed out by Dr. Gray,[372]looks very much like a Phalanger. The orbit is entire as inTupaia. The fingers and toes are five. The one species, called after Sir Hugh Low, G.C.M.G.,P. lowi, is a Bornean animal.
Fam. 3. Centetidae.—This family is entirely confined to the Island of Madagascar. It includes some seven genera. The best-known genus isCentetes.C. ecaudatus, the Tanrec, Tenrec, or Tendrac, is an animal a foot or so in length, without a tail, and with forty-four teeth.[373]The immature animal is so different from the parent as to appear quite a different form. It has three narrow rows of spines along the back, which do not wholly disappear until the permanent dentition has been acquired. Even then the hairs are of a rather spiny character, particularly those upon the back of the head, which are erected when the animal isannoyed. The Tanrec feeds mainly upon earthworms. It is "probably the most prolific of all animals," since as many as twenty-one young are said to have been brought forth at a birth. Some Opossums, however, have twenty-five teats.
Fig. 248.
Fig.248.—Skull of Tenrec.Centetes ecaudatus.fr, Frontal;max, maxilla;pa, parietal;p.max, premaxilla;sq, squamosal. (After Dobson.)
Hemicentetes[374]is a genus with two species. These have spines mixed with the fur of the back. There is no caecum in this or in other Centetidae. The teeth are forty in number, there being only three molars.
Ericulus setosusis a small Insectivore, resembling externally a small Hedgehog. It is covered with close-set spines which, unlike what is found inErinaceus, extend over the short tail. The total number of teeth is thirty-six, the formula being I 2/2 C 1/1 Pm 3/3 M 3/3.
Echinops[375]is another spiny genus which is a stage in advance ofEriculus, for still another molar has been lost, reducing the total number of teeth to thirty-two. The dental formula is thus I 2/2 C 1/1 Pm 3/3 M 2/2. The zygomata are reduced to mere threads.
Microgale, a genus recently instituted by Mr. Thomas, is a small furry Insectivore with a long tail, which is more than double the length of the head and body. There are no less than forty-seven vertebrae in the tail, which is relatively longer than that of any other mammal.
Limnogale, discovered by Forsyth Major, is an aquatic genus, also furry and not spiny, which has departed from the Centetid type and taken to an aquatic life. The single species,L. mergulus, is about the size ofMus rattus; it has webbed toes and a powerful laterally-compressed tail. Clavicles are present, which is not the case withPotamogale.
Oryzoryctesis a Mole-like Centetid. It has fossorial fore-limbs, but a fairly long tail. This genus is furry like the last two. It is said to burrow in the rice-fields and to do much harm. The teeth are forty in number, three incisors and three molars in each half of each jaw.
Fam. 4. Potamogalidae.—This family contains two genera,PotamogaleandGeogale.
Potamogale veloxis a West African animal, which though an Insectivore has the habits of an Otter. It is "somewhat larger than a stoat." The upper surface of the body is dark brown, the belly brownish yellow. It has a flat head and a long tail like the Stoat, but the tail is laterally compressed and very thick. The eyes are very small; the nostril has valves. The toes are not webbed; but the second and third toes are united for the whole length of their first phalanges. Along the outer side of the foot is a thin extension of the integument. In swimming the feet are drawn up along the body, hence webbing would be of no use; but the thin flattening prevents the edge of the foot from acting as a hindrance to the motion of the animal. M. du Chaillu describes it as catching fish, which it pursues with extreme rapidity in the clear mountain streams it frequents; but Dr. Dobson, remarking that no stomachs have been examined, thinks that water insects are more probably its prey. It is not known whether the animal possesses a caecum. The tooth formula[376]is I 3/3 C 1/1 Pm 3/3 M 3/3. The animal is exceptional among the Insectivora in having no clavicles.[377]There are sixteen ribs; there is no zygomatic arch, and the pterygoids converge posteriorly.
Geogale, with one species,G. aurita, is a small representative of this family from Madagascar. It has only thirty-four teeth. When better known it may be necessary, thinks Mr. Lydekker, to make this animal the type of a separate family. The tibia and fibula are distinct, not confluent with one another as inPotamogale.
Fam. 5. Solenodontidae.—This family contains but a single genus.
Solenodon.This genus, including two species, one from Cuba, the other from Hayti, was at one time referred to the Centetidae. It offers, however, numerous points of difference from the members of that family with some general points of agreement. Possibly its isolation in the two West Indian islands mentioned is comparable to the isolation of the Centetidae in Madagascar; they are both survivors of an ancient group of Insectivores extinct elsewhere.Solenodonhas nearly the complete dentition. It has lost only one premolar, and has therefore forty teeth in all. The formula is thus I 3/3 C 1/1 Pm 3/3 M 3/3. It also differs from the Centetidae in having only two inguinal mammae instead of both inguinal and thoracic; the penis of the male does not project from a cloaca, but lies forward. On the other hand, the molars have their cusps arranged in theV-fashion of the Centetidae, a fact, however, which, in the opinion of some, merely points to an ancient trituberculism not indicative of special affinity. It has, moreover, no zygoma in the skull, and there is no caecum. Dr. Dobson has furthermore tabulated a number of differences in muscular anatomy between the two families.Solenodonhas a long naked tail. The snout, always developed in Insectivores, is extraordinarily long in this genus. It is a furry, not a spiny animal.S. cubanusis liable to fits of rage when irritated, a feature which it has in common with Shrews and Moles; it is also stated to have the ostrich-like way of concealing its head in a crevice, "apparently thinking itself then secure." But nothing is known of the genus in a wild state.
Fam. 6. Chrysochloridae.—This family contains only the genusChrysochloris, comprising some five species, all natives of Africa south of the equator. The scientific name of the genus, and also the vernacular name Cape Golden Mole, are derived from the beautiful iridescent hairs which are intermingled with softer and non-iridescent fur.ChrysochlorishasV-shaped cusped teeth like those that are possessed by the Centetidae and Solenodontidae. In the skull as in the Macroscelidae, etc., but not in the Centetidae, there are complete zygomata. They are Moles in habit, and the eyes are covered with skin; the ears, moreover, have no conches. The teeth are forty or thirty-six in number, the reduction being caused by the losing of a molar in those forms which possess the smaller number.[378]It is interesting to notice that theadaptation to a digging life is brought about in quite a different way from that of the true Moles (Talpa). In the latter the fore-limbs are changed in position by the elongation of the manubrium sterni, carrying with it the clavicles, which are extraordinarily shortened (Fig. 251). InChrysochloris, on the other hand, the same need (i.e.that the limbs project as little as possible from the sides of the body, while the length of the limbs is retained, and the leverage of the muscles unaffected) is provided for by a hollowing out of the walls of the thorax, the ribs and the sternum being here convex inwards. The sternum and the clavicles are not modified. The tibia and fibula are ankylosed below. In the manus, moreover, there are but four digits, of which the two middle ones are greatly enlarged. In the Moles there are five fingers, and all are enlarged; there is, too, a great radial sesamoid bone, which is as good as a sixth finger (which, indeed, it is considered to be, in common with similar structures in other animals, by some anatomists). The foot has only four toes.
Fig. 249.
Fig.249.—Golden Mole.Chrysochloris trevelyani.A, Lower surface of fore-foot. × ½. (After Günther.)
Fam. 7. Macroscelidae.[379]—This family contains three genera, all of them African in range, and mainly Ethiopian.
Macroscelides, the Elephant Shrews, are jumping creatures of Shrew-like appearance, combined with a Marsupial look. Both radius and ulna, and tibia and fibula, are ankylosed. Thereare five fingers and toes. There is a caecum as in but few Insectivores. The tooth formula, as revised by Thomas,[380]is I 3/3 C 1/1 Pm 4/4 M 2/(2 or 3), the total number being thus forty or forty-two. There are several species of this genus.
Fig. 250.
Fig.250.—Rhynchocyon chrysopygus.× ¼. (After Günther.)
RhynchocyonandPetrodromusdiffer fromMacroscelidesin not having such long hind-legs. The dental formula of the first is I (1 or 0)/3 C 1/1 Pm 4/4 M 2/2 = 34 or 36, of the latter I 3/3 C 1/1 Pm 4/4 M 2/2 = 40. InPetrodromusthe toes are reduced to four; inRhynchocyonthere are only four digits in the manus as well as in the pes. This animal, as its name implies, has a longish proboscis, which can be bent, and is really very like a miniature Elephant's trunk, and also like that of the Desman (Myogale). It has thirteen pairs of ribs, and a well-developed caecum. Dr. Günther has pointed out that inPetrodromus tetradactylusthe hairs of the lower part of the tail are stiff elastic bristles 5 mm. long, with a swelling at the free tip. The use of this singular modification is not at all apparent.Pseudorhynchocyon, of European Oligocene, is believed to be related to this family.
Fig. 251.
Fig. 252.
Fig.251.—Sternum and sternal ribs of the Common Mole (Talpa europaea), with the clavicles (cl) and humeri (H);M, Manubrium sterni. Nat. size. (From Flower'sOsteology.)
Fig.252.—Bones of fore-arm and manus of Mole (Talpa europaea). × 2.C, Cuneiform;ce, centrale;l, lunar;m, magnum;p, pisiform;R, radius;rs, radial sesamoid (falciform);s, scaphoid;td, trapezoid;tm, trapezium;U, ulna;u, unciform;I-V, the digits. (From Flower'sOsteology.)
Fam. 8. Talpidae.—This family is confined to the Palaearctic and Nearctic regions, or practically so, being fairly equallydistributed as regards genera; a Mole just gets over the boundary into the Oriental region. The genusTalpais entirely Old World in range, and includes several species, of which the Common Mole,T. europaea, is the best known. There are forty teeth, one of the molars of the full mammalian dentition not being represented. In the milk dentition there is an additional premolar, not represented by a successor in the permanent dentition. The formula is thus I 3/3 C 1/1 Pm 4/4 M 3/3. There are no external ears, and the eyes are rudimentary; the soft silky fur is familiar to everybody. The sternum has a strong crest, associated with a powerful development of the pectoral muscles, so necessary to a burrowing animal. The animal, it is hardly necessary to state, lives underground in burrows excavated by itself, which have not, it has been stated, the elaborate and, it appears, fanciful shape assigned to them by many writers. At times Moles appear above ground.Their principal food consists of earthworms, and it may not be out of place to quote Topsell's quaint account of their pursuit of the annelids: "When the wormes are followed by molds (for by digging and heaving they foreknow their owne perdition) they fly to the superficies and very toppe of the earth, the silly beast knowing that the molde, their adversary, dare not followe them into the light, so that their wit in flying their enemy is greater than in turning againe when they are troade upon." It has lately been said[381]that Moles store up earthworms for consumption during the winter, biting off their heads to prevent their crawling away.
Scalops, an American genus, is a Mole-like creature of largely aquatic habits, as its webbed hind-feet show; it has a short, naked tail. Apparently, like the Shrews, it has no lower canines.
Condylura, another American genus, is called the Star-nosed Mole on account of a curious radiating structure at the end of the snout.
Myogale, the Desman, is still more aquatic in habit, and connects the Moles with the Shrews, though, as in many of the former, it has lower canines. It has webbed hind-feet and a long tail. One species occurs in the Pyrenees, the other in Russia. A few other genera (Urotrichus,Uropsilus,Scaptonyx,Dymecodon,Scapasius,Perascalops) belong to the same family.
Fam. 9. Soricidae.—The true Shrews have a much wider range than other families of the present order. In the Palaearctic region are foundSorex,Crossopus,Crocidura,Nectogale,Chimarrogale. The first is also Nearctic, and reaches Central America. In the Ethiopian region is the single peculiar genusMyosorex, butCrociduraoccurs there also.BlarinaandNotiosorexare "Sonoran" in range;SoriculusOriental.Crocidura,Anurosorex, andChimarrogalealso enter this region.Sorexhas teeth tipped with reddish colour, its dental formula being, according to Mr. Woodward's recent researches, I 3/(2 or 3) C 1/0 Pm 3/1 M 3/3 = 32 or 34.
As compared with other Insectivores, therefore, the most remarkable fact found throughout the family is the absence of the lower canines. In addition to this the genus may be known—the family indeed—by the large size of the first pair of incisors. In the above formula it is possible, thinks Mr. Woodward, that there may be errors; he is not certain whether the supposedupper canine may not be a fourth incisor, and whether the first premolar may not be really the canine. Another peculiar feature about the dentition ofSorexis the suppression of the teeth of the milk dentition, which are functionless, and probably uncalcified. The genusSorexis terrestrial. The tail is long and covered with hairs. There are two species in this country,S. vulgarisandS. minutus. The former is the Shrew of legend and superstition; and it is no doubt the species that has lent its name to the more untameable members of the softer sex, though it is the males which are especially pugnacious. As to legend, everybody has heard of the shrew ash whose leaves, after a Shrew has been inserted living into a hole cleft in the tree, are a specific for diseases of cattle, caused by the Shrew itself creeping over them.
The Rev. Edward Topsell, author ofThe Historie of Four-footed Beastes, who defends his veracity by asserting that he does not write "for the rude and vulgar sort, who being utterly ignorant of the operation of learning, do presently condemne al strange things," says of the Shrew that "it is a ravening beast, feigning itself gentle and tame, but, being touched, it biteth deep and poysoneth deadly. It beareth a cruel minde, desiring to hurt anything, neither is there any creature that it loveth, or it loveth him, because it is feared of all." It is probable that all this rustic feeling is due to the powerful effluvium which the Shrew undoubtedly emits.
S. minutushas the distinction of being the smallest British mammal; it is scarcer than the last. This form is found upon the Alps, as is also the peculiarly Alpine speciesS. alpinus, which inhabits the Alps, Pyrenees, Carpathians, and the Hartz.
Crossopus fodiens, the Water Shrew, has also brown-stained teeth. It is not uncommon in this country, and lives in burrows excavated by the sides of the streams which it affects.
Besides these two genera,Soriculus,Blarina, andNotiosorexhave red-tipped teeth. InCrocidura,Myosorex,Diplomesodon,Anurosorex,Chimarrogale, andNectogalethe teeth are white-tipped. These are all the genera of the family allowed by the late Dr. Dobson in a review of that family.[382]
ChimarrogaleandNectogaleare aquatic genera. The formerconsists of a Himalayan and Bornean, and of a Japanese species, which have not webbed feet, but have a tail with a fringe of elongated hairs.
Nectogale elegansis one of the characteristic animals of the Thibetan plateau. It has webbed feet. The teeth are as inChimarrogaleI 3/2 C 1/0 Pm 1/1 M 3/3.
The other genera are terrestrial in habit.
Fig. 253.
Fig.253.—Galeopithecus volans.× ⅓. (After Vogt and Specht.)
The familyGaleopithecidaecontains but one genus, which has been at times referred to the Lemurs, to the Bats, or has been made the type of a special order of mammals. It is better to regard it as an aberrant Insectivore—so different indeed from other forms that it requires a special sub-order for its reception.
Galeopithecus[383]inhabits the Oriental region. It is a larger animal than any other Insectivore, about the size of a Cat, and has a patagium extending between the neck and the fore-limb, between the fore-limb and the hind-limb, and between the hind-limb and the tail. This patagium is abundantly supplied with musculature, but the fingers are not elongated as in the Bats for its support. In the degree of its development, however, the patagium of this creature is midway between that ofSciuropteruson the one hand, and the Bats on the other. It presents many remarkable features in its organisation. The brain is like that of the Insectivora in the exposure of the corpora quadrigemina by the slight extension backward of the cerebral hemispheres; but its upper surface is marked by two longitudinal furrows on each side, a state of affairs (in combination) which is unparalleled among the Mammalia. The teeth are peculiar by reason of the singular "comb-like" structure of the lower incisors. This, however, is an exaggeration of what is to be found inRhynchocyonandPetrodromus, while the same style of tooth, though not so highly developed, characterises certain Bats. The Tupaiidae and certain Lemurs show what Dr. Leche regards as the beginning of the same thing. As inTupaiaalso there is an indication of the characteristically Lemurine sublingua. The stomach is more specialised than in other Insectivores, the pyloric region being extended as a narrowish tube. There is a caecum. A peculiarity of the intestinal tract is that the large intestine is longer than the small.
We may thus define the Bats:—Flying mammals, with the phalanges of the four digits of the hand following the pollex greatly elongated, and supporting between themselves and the hind-limbs and tail a thin integumental membrane, which forms the wing. The radius is long and curved; the ulna rudimentary. The knee is directed backwards, owing to the rotation of the limb outward by the wing membrane. From the inner side of the ankle-joint arises a cartilaginous process, the calcar, which supports the interfemoral part of the wingmembrane. The mammae are thoracic; the placenta discoidal and deciduate. The cerebral hemispheres, which are smooth, do not extend over the cerebellum.
Fig. 254.
Fig.254.—Barbastelle.Synotus barbastellus.× ½. (After Vogt and Specht.)
This large order of mammals was once placed with the Primates. There is no doubt, however, that they form a perfectly distinct order; no knowledge of fossil forms in any way bridges over the gap which distinguishes them from the highest mammals. The most salient feature in their organisation is clearly the wings. These consist of membrane, an expansion of the integument, provided with nerves, blood-vessels, etc., which mainly lie stretched between the digits 2 to 5. These digits themselves, which are enormously elongated, act like the ribs of an umbrella, and when the wing is folded they come into contact. Besides this part of the flying apparatus there is a tract of membrane lying in front of the arm, which corresponds to the wing membrane of the bird, but which in the Bats takes quite a subordinate place. In the bird, on the other hand, there is a metapatagium, which is the main part of the wing of the Bat. It seems just possible that inArchaeopteryxthe metapatagium was more Bat-like. Furthermore, a steering membrane, like that which fringes the tail in some Pterosaurians, lies interfemorally in Bats, and includes the whole or a part of the tail. The pollex takes no share in the wing, but projects, strongly armed with a claw, from the upper margin.
The bones of this order of mammals are slender and marrowy; they are thus light, and subserve the function of flight. A most remarkable feature among the external characters of the Bat tribe is the extraordinary and often highly complicated membranes which surround the nostrils. These are at least oftenmore strongly developed in males than in females, and may perhaps be partly relegated to the category of secondary sexual characters. But it seems that they have also an important tactile function, and enable the creatures to fly without touching bodies which intrude themselves upon their way. The ears, too, are frequently very large, and it may be supposed that the sense of hearing is correspondingly acute. In the common Long-eared Bat of this country, the ears are not greatly inferior in length to the head and body of the animal combined. The ears are of every variety of shape, and offer characters which are valuable in the systematic arrangement of the members of the order.
Fig. 255.
Fig.255.—Skeleton of Flying Fox.Pteropus jubatus.× ⅛. (After de Blainville.)
In the skull of Bats there is very rarely a complete separation between the orbital and temporal fossae; the lachrymal duct is outside the orbit. The tympanics are annular, and in a rudimentary condition. The centraof the vertebrae tend to become ankylosed in old individuals; the caudals have no processes, but are like those quite at the end of the series in long-tailed animals. The sternum is keeled for the better attachment of the pectoral muscles, the chief muscles of flight. The ribs, which are much flattened, are occasionally ankylosed together by their margins. There is a well-developed clavicle. In the carpus the scaphoid, lunar, and cuneiform are all fused together. In the hind-limb the fibula is rarely fully developed.
The Bats are divisible into two primary groups, which are those of the Megachiroptera and the Microchiroptera.
Fig. 256.
Fig.256.—Skull ofPteropus fuscus. ×3⁄2. (After de Blainville.)
ThePteropodidaeare frugivorous Bats, usually of large size. The chief distinguishing feature is the fact that the molars are not tubercular, but marked with a longitudinal furrow, which is, however, concealed in the genusPteralopexby cusps. The palate is continued back behind the molars. The index finger has three phalanges, and is usually clawed. The ears are oval, and the two edges are in contact at the base of the ear. The tail, if present, has nothing to do with the interfemoral membrane. This group is entirely Old World in range. The genusPteropusembraces the creatures known as Flying Foxes. They are the largest forms in the sub-order, sometimes having an expanse of wing of 5 feet (this is the case withP. edulis). The muzzle is long, and the face therefore "foxy" in appearance.The inner margin of the nostrils projects, a preparation for the tubular nostrils ofHarpyia. The tail is absent. The premolars are three and the molars two. The pyloric region of the stomach is extended and twisted upon itself. Of this genus there are nearly sixty species, extending from Madagascar to Queensland. Thirty species inhabit the Australian, twenty the Oriental region. Madagascar has seven, and one species just enters the Palaearctic. The occurrence of this genus in India and in Madagascar is one of those facts which favour the view supported, on these and other grounds, by Dr. Dobson and Dr. Blanford that a connexion between India and Madagascar must once have existed; for these slow-flying creatures could hardly be believed capable of traversing vast stretches of ocean by their unaided efforts.[384]
Fig. 257.
Fig.257.—Flying Fox.Pteropus poliocephalus.× ⅓.
Pteropusis represented in the Ethiopian region by the allied genusEpomophorus. Of this there are perhaps a dozen species. The teeth are reduced to two premolars in the upper jaw,three remaining below; while there is but one molar in each upper jaw, and two in each lower. Dr. Dobson has studied the structure of the remarkable pharyngeal sacs which exist in the neck of the male, and are capable of inflation.
Pteralopexof the Solomon Islands has shorter ears than have manyPteropus, otherwise its external characters are the same. As inPteropus nicobaricus, this genus has the orbits shut off by a bony ring, an extremely rare phenomenon in Bats. The canines have two cusps. The characters of the grinding teeth have already been mentioned. It is uncertain whether the only species of this genus,P. atrata, is, or is not, a vegetable feeder.Harpyiahas shortish ears and extraordinarily prolonged and tubular nostrils. There is a hint of the accessory cusp to the canines mentioned above inPteralopex. The incisors are reduced to one on each upper jaw, and none below.Cynopterushas also often bituberculate canines. It is an Oriental genus with several species.
Nesonycteris, with one species from the Solomon Islands,N. woodfordi, has the dental formula I 2/1 C 1/1 Pm 3/3 M 2/3. The index finger has no claw; the tail is absent. The premaxillae are separated anteriorly.
Eonycteris, with a single cave-dwelling species from Burmah,E. spelaea, has also no claw upon the index; the tooth formula is fuller by reason of the presence of an additional incisor below. The tongue is very long and is armed with papillae. There is a short but distinct tail.
Notopteris, from New Guinea and the Fiji Islands, is distinguished from the related genera by its long tail.
The remaining genera of Fruit Bats areBoneia,Harpyionycteris,Cephalotes,Callinycteris, andMacroglossus, from the Oriental region, andScotonycteris,Liponyx, andMegaloglossusfrom the Ethiopian region; finally, there is the AustralianMelonycteris.
The members of this sub-order are mostly insectivorous though occasionally "frugivorous or sanguivorous" Bats. The molars are multicuspid with sharp cusps. The palate is not continued back behind the last molar. The second finger has but one phalanx, ornone; occasionally there are two. It has no claw. The ear has its two sides separate from their point of origin upon the head. The group is of Old-World distribution.
Fam. 1. Rhinolophidae.—The Bats of this family possess the leafy outgrowths around the nostrils. The ears are large, but have no tragus. The index finger has no phalanx at all. The premaxillary bones are quite rudimentary, and are suspended from the nasal cartilages. In addition to the pectoral mammae they have two teat-like processes situated abdominally. The tail is long, and extends to the end of the interfemoral membrane.
The genusRhinolophushas a large nose leaf, and an antitragus to the ear. The first toe has two joints, the remaining toes have three joints each. The dentition is I 1/2 C 1/1 Pm 2/3 M 3/3. There are nearly thirty species of the genus, which are restricted to the Old World. Two species occur in this country, viz.R. ferrum equinum, the Great Horse-shoe Bat, and the Lesser Horse-shoe Bat,R. hipposiderus. The name is of course derived from the shape of the nose leaf.
The genusHipposiderusand some allied forms are placed away fromRhinolophusand its immediate allies in a sub-familyHipposiderinae. The type genusHipposiderus, or, as it ought apparently to be called,Phyllorhina, is Old World in range, like all the other members of the family.
The nose leaf is complicated, and there are only two phalanges in all the toes; there is no antitragus to the ear. A curious feature in the osteology of the genus, and indeed of the sub-family, is the fact that the ileo-pectineal process is connected with the ilium by a bony bridge; this arrangement is unique among mammals.
The genusAnthops, only known from the Solomon Islands, and represented there by but a single species (A. ornatus), has an extraordinarily complicated nose leaf. The tail, like that of the OrientalCoelops, likewise represented by a single species (C. frithii), is rudimentary.
Triaenops, Ethiopian and Malagasy, has, like the AustralianRhinonycteris, a well-developed tail.Triaenopshas also a highly-complicated nose leaf.
Fam. 2. Nycteridae.—This family is to be distinguished from the Rhinolophidae by the fact that the ear has a small tragus, and by the small and cartilaginous premaxillae. In addition tothese two characters it may be added that the nose leaf is well developed, but is not so complicated as in the last family. The type genusNycterisis Ethiopian and Oriental, nine species being African, and only one,N. javanica, being, as the specific name denotes, from the East.Megadermais to be distinguished by the loss of the upper incisors. There is no tail, and the ears are particularly large. They are carnivorous Bats, andM. lyra, called the "Indian Vampire Bat," chiefly affects frogs as an article of diet.
Fam. 3. Vespertilionidae.—This family has not the nose leaf of other families. The apertures of the nostrils are simple, round, or crescentic apertures. The ear has a tragus, and the tail is not produced to any great degree behind the interfemoral membrane. There are two phalanges to the index digit.
This family in numbers of species is vastly in excess of any other family of Bats. The most recent estimate, that of P. L. and W. L. Sclater, allows 190. But the generic types are by no means so numerous as in the Phyllostomatidae. This is a significant fact when we reflect upon the geographical range of the two families. The Vespertilionidae range over the whole earth, while the Phyllostomatidae are practically limited to the South American continent, only just getting into the Nearctic region. They inhabit, therefore, a more restricted area, and, in consequence of competition, have specialised more freely than the widely-spread and therefore not crowded Vespertilionidae.
The genusVesperugois by far the largest genus of this family, embracing no less than seventy species. The tail is shorter than the head and body together; the ears are separate, and moderate or short in size; the tragus is generally short and obtuse. The dentition is I 2, C 1, Pm 2 or 1, M 3. It is a remarkable fact that this genus, unlike most Bats, produces two young at a time. The genus is universal in range, and one species, the Serotine Bat, known in this country, even ranges from the New World to the Old; but with so small a creature the possibility of accidental transportation by man must not be left out of sight. The British species are—V. serotinus, the Serotine already mentioned;V. discolor, a single example only of which has occurred, and may have been introduced;V. noctula, the habits of which were described by Gilbert White;V. leisleri; and the Pipistrelle,V. pipistrellus, which is the best-known member of the genus in this country.
The genusVespertiliocontains some forty-five species, and is world-wide in range. It has one more premolar in the upper jaw than hasVesperugo. There are no less than six British species, of whichV. murinusis the largest species of Bat recorded from this country, but is not quite certainly indigenous.
Plecotushas very long ears. The dentition is I 2/3 C 1/1 Pm 2/3 M 3/3. The tragus is very large. There are but two or possibly three species, of which one is North American, and the other is the Long-eared Bat,P. auritus, of this country, but ranging as far as India. The shrill voice, inaudible to some ears, of this Bat has been heardofby everybody.
Synotusincludes the British Barbastelle,S. barbastellus, as well as an Eastern form. It differs from the last genus principally by the loss of a lower premolar. The ears, too, are not so large.Otonycteris,Nyctophilus, andAntrozousare allied genera; the last is Californian, the others Old-World forms.
Kerivoula(orCerivoula) has a long, pointed, narrow tragus. The tail is as long as or longer than the head and body. The dentition is as inVespertilio; but the upper incisors are parallel instead of divergent as in that genus. The brilliantly-colouredK. pictais, on account of this very fact, the best-known species. The nameKerivoula, a corruption of the Cinghalese "Kehel vulha," signifies plantain bat. This Bat has been described as looking, when disturbed in the daytime, more like a huge butterfly than a Bat, which is naturally associated with sombre hues. Other species occur in the Oriental, Australian, and Ethiopian regions.
Miniopterushas a premolar less in the upper jaw; it has a long tail as in the last genus. One species,M. scheibersi, has almost the widest range of any Bat, it being found from South Europe to Africa, Asia, Madagascar, and Australia.
Natalusis an allied form from Tropical America and the West Indies. It is chiefly to be separated fromKerivoulaby the short tragus to the ear.
Thyropterais also South American. It is distinguished by the curious sucker-like discs upon the thumb and foot. These "resemble in miniature the sucking cups of cuttle-fishes." The Madagascar genus,Myxopoda, with but one species, has also an adhesive but horse-shoe-shaped pad upon the thumb and foot.
Scotophilushas shortish ears with a tapering tragus. The tail is shorter than the head and body, and is nearly contained withinthe interfemoral membrane. The dentition is I 1/3 C 1/1 Pm 1/2 M 3/3, with another upper incisor in the young. It is African, Asiatic, and Australian.
This genus appears to be connected withVesperugoby Mr. Dobson's proposed genus, or sub-genus as it is generally held to be,Scotozous.[385]The genusNycticejus, founded for the inclusion ofScotozous dormeri, an Indian species, should, according to Dr. Blanford, replace on grounds of priority the nameScotophilus. But as this name (Nycticejus) is one introduced by Rafinesque, whose work was so uncertain and untrustworthy, it seems preferable to retain the better-known name ofScotophilus, introduced by William Elford Leach.
The genusChalinolobus[386]has short, broad ears with an expanded tragus. A distinct fleshy lobule projects from the lower lip on either side of the mouth. The tail is as long as the head and the body. The dental formula is I 2/3 C 1/1 Pm 2/2 or 1/2 M 3/3. The genus occurs in Africa, Australia, and New Zealand; but the African species, with diminished premolars and pale coloration, have been distinguished asGlauconycteris.
Fam. 4. Emballonuridae.—The Bats belonging to this family have no nose leaf. The tragus is present, but often very small. The ears in this family are often united. There are two phalanges in the middle finger. The tail is partly free, either perforating the interfemoral membrane and appearing upon its upper surface, or prolonged beyond its end. The face is obliquely truncated in front, the nostrils appearing beyond the lower lip.
Emballonurais Australian, Oriental, and Mascarene in range. The ears arise separately, and there is a fairly developed and narrow tragus. The tail perforates the interfemoral membrane. The dental formula is I 2/3 C 1/1 Pm 2/2 M 3/3.
Rhinopomahas the ears united; the incisors are reduced by one on each side of each jaw, and the premolars are similarly reduced, but only in the upper jaw.
Noctiliois an American genus of two or three species, which has one pair of markedly large upper incisors, which completely conceal the outer pair. On these grounds this Bat was removed from its allies and placed by Linnaeus among the Rodents, an instance of the disadvantage of the artificial scheme of classification. The species namedN. leporinushas been shown to feed upon fish.
Furia,Amorphochilus,Rhynchonycteris,Saccopteryx,Cormura, andDiclidurusare other Neotropical genera of the same family.
The genusTaphozous[387]has a tail which perforates the interfemoral membrane, appearing on its upper surface; it is capable of being withdrawn. The premaxillaries are cartilaginous. The dentition is I 1/2 C 1/1 Pm 2/2 M 3/3. The upper incisors often disappear. Many species of the genus have a gular sac, opening anteriorly between the jaws. This is better developed in the males. The genus ranges from Africa through Asia to New Guinea and Australia. There are some twelve species.
The genusMolossus[388]has short legs and well-developed fibulae. The tail is thick and fleshy, and is prolonged far beyond the margin of the interfemoral membrane. The ears are united together above the nose; the tragus is minute. The dentition is I 1/1 or 1/2 C 1/1 Pm 1/2 or 2/2 M 3/3. This genus, which is confined to the tropical and subtropical portions of America, has long and narrow wings. The Bats can thus fly rapidly, twist about with ease, and capture strongly-flying insects. There are a large number of species.
Nyctinomusis an allied genus, and also has many species. These range through both hemispheres. The chief differences fromMolossusare that the premaxillary bones are separate in front or united by cartilage, and that the incisors may be three in the lower jaw.
Fam. 5. Phyllostomatidae.—The Bats of this family are extremely numerous and almost entirely confined to South America. None of them occur outside the New World. There are some thirty-five genera. The members of the family are to be distinguished by the presence of the nose leaf, by the well-developed premaxillae, and by the possession of three phalanges by the middle finger. They are large, and the tragus of the ear is well developed.
Vampyrusof South America contains the large species V. spectrum, which, mainly on account as it seems of its "forbidding aspect," was supposed to be a bloodsucker. This genus has two incisors on each side of the upper jaw.
The genusGlossophagarepresents another type of structure in this family. The tongue is long and extensile, and is much attenuated towards the tip, where it is covered with strong and recurved papillae. This structure was at one time thought to indicate abloodsucking habit; but its use appears to be merely that of scooping out the soft insides of fruits, upon which the Bat mainly lives. The incisors are only one on each side of the upper jaw. The really bloodsucking Bats of this family belong to the generaDesmodusandDiphylla. The former is the Vampire, the species being known asDesmodus rufus. These Bats have no tail; there is no true molar tooth; the canines are large, and the single pair of upper incisors quite caniniform, and very sharp and strong. These are the main teeth for aggression. In accordance with its diet of blood, the Vampire has a peculiarly modified intestine. The gullet is provided with a bore so small that nothing but fluid food could pass down it; the stomach is intestiniform in shape.
The highest of mammals, the Primates,[389]may be thus differentiated from other groups:—Completely hairy, generally arboreal mammals, with five digits on fore- and hind-limbs, provided with flat nails (except in the case of certain Lemurs and the Marmosets), the phalanges that bear these being flattened at the extremity and expanded rather than diminished in size. The fore-feet are grasping hands as a rule, and the hind-feet walking as well as (generally) grasping organs, and the mode of progression is plantigrade. The teats, except inChiromys, are thoracic, and even axillary in position. The skull is characterised by the fact that the orbital and the temporal vacuities are, at least partly, separated by bone. The clavicles are always present. The carpus has separate lunar and scaphoid bones, and the centrale is often present. There is rarely an entepicondylar foramen in the humerus, except in some archaic Lemurs. The femur has no third trochanter. The stomach is usually simple, being sacculated only in Semnopithecinae. The caecum is always present, and often large.
This great group could be easily divided into two separate orders, the Apes and the Lemurs, if it were not for certain fossil types. As will be seen from the description ofNesopithecusand ofTarsius, the actual hard and fast lines betweenallApes andallLemurs are very few. On the other hand, it is a little difficult to draw a hard and fast line between the Primates as a whole—or at least between the Lemurine section—and the Creodonta, agroup to which so many others appear to converge. It is disputed, for example, whether the Chriacidae among extinct Lemurs are rightly placed, or whether they should be referred to the Creodonta. The number of primitive characters seen among the Primates, even in Man himself, is remarkable. Of these the more important are the five digits of both limbs and the plantigrade walk, the presence of clavicles and of a centrale, and the absence of a third trochanter. All these features distinguish the early Eutheria.
The animals known as Lemurs, from their nocturnal and ghostly habits, are on a lower level of organisation than the other division of the Primates. Even the external form enables the members of the present sub-order to be readily distinguished from the higher Anthropoidea. The head is more like that of a Fox, with a sharp muzzle; it lacks the human expression of the face of even the lower among the Apes. The long tail is never prehensile, and there is never any trace of cheek pouches or of integumental callosities, which are frequently so characteristic of the Apes. The Lemurs agree with the remainder of the Primates in having pectoral mammae (sometimes abdominal ones are present in addition, and inHapalemur—in the male at least—there is a mamma upon each shoulder), in having opposable thumbs and toes, and in the flattened digits. The tail varies from complete absence (in theLoris) to a great length and bushiness in the Aye-aye. The pectoral limbs are always shorter than the hind-limbs; the reverse is occasionally the case in the Anthropoidea. A curious contrast between the two divisions of the Primates concerns the digits of the hands and feet. In the Anthropoidea it is the hallux or pollex which is subject to great variation. In the Lemurs, on the contrary, the thumb and great toe are always well developed, but the second or the third digit constantly shows some abnormality; thus the singular elongation of the third digit of the hand inChiromysand the absence of the index in thePotto.[391]In all Lemurs thesecond toe is furnished with a sharp nail, unlike the flattened nails of the other fingers and toes, and inTarsiusthe third also is thus provided. As to osteology, the shape of the head, already referred to, indicates some of the differences in the skull which mark off the Lemurs from the Anthropoidea. The brain case is small relatively to the face; the orbital and temporal fossae are in communication, though the frontal and jugal bones are united behind the orbit. The two halves of the lower jaw are not invariably ossified to form one piece, as is the case with most Apes. The lachrymal foramen lies upon the face in front of the orbit. The teeth are characteristic, not so much in their number (the dental formula is usually I 2, C 1, Pm 3, M 3 = 36) as in the disposition of the incisors. The incisors of the lower jaw and the canines project forwards in a way only found in a few American Monkeys; as in the Apes there are four incisors in each jaw, but, with the exception of the highly aberrantChiromys, there is a space in the upper jaw between the incisors of the two sides. The canines of the lower jaw, moreover, are often incisiform. There is a well-developed sublingua beneath the tongue (see p.61). The stomach is perfectly simple; and the caecum, always present and varying in length, never has a vermiform appendix. The gall-bladder is always present. The brain differs from that of the Anthropoidea in that the cerebellum is, as in the lower Mammalia, exposed. The convolutions upon the cerebral hemispheres are not greatly developed, a circumstance, however, which (see p.77) may have more relation to the size of the animals than to their mental development. Though the brain in its general outlines is not like that of the other Primates, there are certain resemblances; the most striking of these is perhaps the presence, though in rather a rudimentary condition, of the "Simian fissure."
The Lemurine brain has been chiefly studied by Flower,[392]by Milne-Edwards,[393]and by myself.[394]There are also a number of scattered papers dealing with particular types, such as the memoirs of Owen[395]and Oudemans,[396]upon the brain (and the general anatomy) ofChiromys. Without going into greatdetail it may be stated generally that the anatomy of the brain of this group confirms the classification which is adopted in this work.
A curious feature in the anatomy of the Lemurs, which they share with animals so remote from them in the system as the Edentata, is the breaking up of some of the arteries of the limbs to form retia mirabilia; nothing of the kind is known among the other Primates.
Perhaps the most remarkable difference between the Lemurs and the Anthropoidea, which are really in many respects more closely allied than might be inferred from the above summary of differences, is in the structure of the placenta. The Lemurs agree with the Ungulates in having a non-deciduate placenta.
A curious feature confined to the sub-family Lemurinae was first discovered by myself inHapalemur griseus.[397]On the forearm (see Fig. 258) is an area of hardened skin, which is raised into spine-like processes. Fully developed, this organ is characteristic of the male, the area being marked off in the female, but without the spiny outgrowths. On removing the skin a gland about the size and shape of an almond is brought into view. In other Lemurs there is no modified skin, but a small tuft of particularly long hairs, which are also present inHapalemur, and a small gland beneath the skin. The gland ofHapalemurmay be comparable with a tract of hardened skin inLemur catta, which projects to a large extent and has been spoken of as a "climbing organ."
An almost exactly similar tuft of spine-like outgrowths exists upon the lower end of the ankle ofGalago garnetti. The spines are black and bent, just as they are inHapalemur. There appears also to be a gland. This structure is not universal in the genusGalagoany more than is the patch of spines in the genusHapalemur.
In addition to this gland and to the patch of spines which cover it, the same Lemur as well asChirogaleusand certain species ofLemurpossess to the inner side of it a bundle of long and stiff bristles associated with unusually large sebaceous glands; these structures are, of course, not homologous with the gland of the arm ofHapalemur, as they coexist in the samespecies. They are, moreover, not peculiar to the Lemurs, but exist in the Squirrel, in the Domestic Cat, in the Leopard, inBassaricyon,[398]the Otter, various Marsupials, and doubtless in many mammals which require a tactile organ, for these hairs are associated with a large branch of the radial nerve.