Cyclops quadricornis.(Fig. 1, highly magnified; fig. 2, natural size.)
Cyclops quadricornis.(Fig. 1, highly magnified; fig. 2, natural size.)
“These little crustaceous animals may be found at all seasons of the year, near the surface of the water; they are, however, most abundantin July and August. I have collected great numbers of them on a warm day in the latter month, with a small cloth net, immersing it about an inch below the surface. They are mostly colourless in ponds covered with herbage, but in small collections of rain water, on a loamy soil, are of a fine rich colour.
“The body of this creature is covered with crustaceous or shelly plates, which overlap each other, and admit both of a lateral and vertical motion between them. Their ends do not meet on the side, but have sufficient space between them for the insertion and play of the organs of respiration. The rostrum, or beak, is short and pointed: it is a prolongation of the first segment which forms the head. A little above the beak, a single eye is imbedded beneath the shell, of a dark crimson colour, nearly approaching to blackness. The true form of this organ it is difficult to determine. Mr. Baker gives it the shape of two kidney-beans placed parallel to each other, and united at their lowest extremities. When viewed laterally, it appears round, while in some other positions it is square.”
The eggs are curiously placed in two bags, presenting an appearance similar to clusters of grapes, and of considerable magnitude, compared with the size of the animal. These egg-bags are seen in the engraving, (which represents a female,) projecting from each side of the hinder portion of the shell. The centre of each egg is of a deep opaque colour, which in some specimens is green, in others red.
The young of the Cyclops, when first excluded from the egg, are extremely minute, and so different from the mother, that Müller has described them as forming two distinct genera.
This species of the Water Flea differs from the last, in having its body divided into a greater number of segments; it is also much smaller; it is equally active with that last described, but its form renders it more graceful in its motions. “These little creatures,” says Mr. Pritchard, “seem to possess great discernment and cunning; for, if approached, they remain motionless on the plant on which they reside, in the apparent hope that they may be overlooked; but when a fit opportunity occurs, they suddenly bend the body, and spring away with a kind of vaulting leap.”
Cyclops minutus, much magnified.
Cyclops minutus, much magnified.
They inhabit the various species of confervæ, and may often be met with in great numbers on the stalks and underside of healthy duckweed, growing on the surface of the water. They are most numerous in Apriland May, and disappear as the heat of the season increases. They will not live in stagnant water containing much decomposed vegetation, and require, therefore, to be kept for observation in a large vessel of clean water. They are easily caught after a shower of rain, on the under surface of the duckweed, by taking out a little with a basin or cloth net. When found, they appear busily engaged in search of prey, moving about with great activity, and examining every portion of the plant in the most scrutinizing manner. In this pursuit the body is not bent as in the magnified representation in the engraving, but is kept in a straight crawling position. Their natural length is about the three hundredth part of an inch.
The female of the last species has two outward receptacles for the eggs; in this there is but one, and that is placed on the under part of the animal near the tail.
These singular little creatures are found in stagnant fresh water: they are very small, and, at first sight, appear like a bivalve shell. The animal which is enclosed in this two-valved case, opens and shuts it at will; when it does this, it throws out from one end of the shell numerous whitish hair-like members; it is by moving these that it is enabled to swim with considerable celerity, and it never stops until it meets with some object on which it can rest. Its two antennæ, which issue from the fore part of the shell, are long, very flexible, and bent backwards; their articulations are numerous, which gives them great freedom of motion. The movements of these antennæ contribute materially to the swimming powers of the creature.
At the place where the head is united to the body, a small black point is seen,—this is the eye of the animal.
Cypris pubera.(Fig. 1, highly magnified; fig. 2, natural size.)
Cypris pubera.(Fig. 1, highly magnified; fig. 2, natural size.)
The Cypris changes its shell like the rest of the Crustacea; it is found in marshes where vegetable substances are growing. Sometimes they are so numerous, that the water appears covered with them; they are more usually found in Spring and Autumn than at any other part of the year; from this it is inferred that there are two broods in the course of the year.
The drying up of marshes during the Summer heats, destroys immense numbers every season. It appears, however, from observation, that in this case, some of these tiny creatures manage to bury themselves in the mud, where they hermetically close their shells, and remain in a kind of dormant state, until rain or other causes have again filled the marshes with water.
A species nearly allied to this, theArtemia Salina, the Lymington shrimp, or brine-worm, is able to live in the brine of the salt-pans, which is so strongly impregnated with salt, as to destroy any other Crustaceous animal.
Myriads of these animalculæ are to be found in the salterns at Lymington, in the open tanks or reservoirs, where the brine is deposited previous to boiling. A pint of this brine contains about a quarter of a pound of salt. These tanks are called clearers, as the liquor becomes clear in them, an effect which the workmen attribute, in some degree, to the rapid and continual motion of the brine-worm, or the particles which cloud the liquor serving for its food; but this is mere conjecture. So strongly persuaded, however, are the workmen of this fact, that they are accustomed to transport a few of the worms from another saltern if they do not appear at their own. They increase astonishingly in the course of a few days.
It is observable that the brine-worm is never seen in the sun-pans, where the brine is made by the admission of sea-water during the Summer, and which are emptied every fortnight; but only in the pits and reservoirs, where it is deposited after it is taken out of the pans, and where some of the liquor constantly remains, when it becomes much diluted with rain water. From October till May, (during which time the manufacture is at a stand,) a few only of the worms are visible; but at the approach of Summer, young ones appear in great numbers.
THE END.
London:
John W. Parker, St. Martin’s Lane.