3004. In the antagonism of the amnion the integument is evolved, and in its antagonism the branchiæ and lungs.
3005. In obedience to the antagonism of the arteries and veins, the vitelline sac divides into small and large intestine. The one pursues a course towards the arterial extremity of the body, the brain, the other towards the venous or sexual parts; mouth and anus.
3006. Finally, from the antagonism of the allantois the sexual parts emerge at the very extremity of the body, which is placed opposite to the mouth.
3007. The osseous and muscular system first makes its appearance, when the vegetative parts are present.
3008. The intestines, the vessels, and the commencement of the sexual parts are originally situated in the umbilical cord, which is itself surrounded by the integument. The umbilical cord is therefore nothing else than the posterior extremity of the body or abdomen, through which the embryo respires and is nourished.
3009. The first respiration and deglutition is therefore a respiration and deglutition effected by the sexual parts, as in the lowest animals.
b.Functions of the Fœtus.
1.Nutrition.
3010. The juices which are contained in the developmental sacs are nutritive juices or chyle; they contain principally albumen. The chyle of the intestinal vesicle depends upon the vitellus.
3011. The fœtal water in the amnion is derived from albumen in the ovum; it is here secreted by the oviduct, but in the Mammalia by the internal wall of the uterus, and absorbed by the general envelopes.
3012. The cause of this secretion resides in the decomposition of the blood through the influence of the chorion. Thus if the maternal blood become deoxydized, it must necessarily revert to the condition of chyle. This chyle is the fœtal water.
3013. The fœtal water is absorbed by the embryo through the integument.
3014. No blood is transferred from the mother directly to the fœtus.
3015. The blood-vessels of the uterus and placenta do not open into or communicate with each other.
3016. The fœtal water corresponds to the albumen or the white of eggs, not to the vitellus. This becomes also during incubation consumed in the formation of the body of the chick, and not the vitelline mass, which is first of all destined for the intestine.
3017. Towards the termination of pregnancy, when the fœtus is endowed with muscular motion, the fœtal water is also absorbed. Nutrition is therefore in the commencement an absorption carried on by the integument, and lastly by the intestine.
2.Respiration.
3018. The respiratory organ of the fœtus is the chorion, and in particular the placenta. Its tissue is like that of the branchiæ or spleen.
3019. The arterial blood transmitted through the umbilical vein is conducted through the foramen ovale into the left ventricle of the heart, and from thence directly to the principal organ of the fœtus, the brain and spinal cord. From hence it returns, venous in quality, to the right side of the heart, and from thence through the ductus arteriosus into the inferior or descending aorta, from which, pursuing its course through the umbilical arteries, it again reaches the placenta, in which it undergoes a renewed oxydation.
3020. If therefore the umbilical cord be compressed, the fœtus dies suddenly, as happens indeed accidentally in certain cases, which completely resemble those of death produced by suffocation. The chick when in the egg dies, if the egg-shell be coated over with varnish, or if the egg be submitted to the noxious influence of gases which are devoid of oxygen.
3021. The respiration effected through means of the placenta, admits also of being proved by the sudden change which occurs in the circulation after birth. No arterial blood being then any longer brought to the heart through the umbilical vein, the left heart is no longer stimulated, and the foramen ovale collapses and is closed. Thus, all the blood enters the right side of the heart, and finding no thoroughfare into the ductus arteriosus, it is driven forcibly into the lungs, which now expand, and thereby leave an empty space between the pulmonary vessels, into which the air rushes in.
3022. The first act of respiration is therefore theresult of the lungs being injected with venous blood, and thus of necessity ensues. When, on the contrary, cases arise causing pulmonary suffocation, the blood then regurgitates to the umbilical vessels, in order to reach the original branchia or placenta.
3023. Another process of respiration is found to take place in the vessels of the allantois. Its fluid becomes oxydized and penetrates through the urinary cyst into what have been called primordial kidneys. This kind of respiration through the anus is persistent in many Worms and larvæ of Insects.
3024. Finally, there is a respiratory process on the body of the embryo itself through the branchial apertures on its neck; these in the Frogs and Salamanders still continue visible after their exclusion from the egg. This oxygen must be derived from the fœtal water.
3025. Without doubt also the vitelline vessels respire, and thus each vegetative system has its own process of respiration. The intestine respires through the vitelline vessels, the vascular system through the vessels of the chorion, the sexual system through those of the allantois, the integument through the branchial apertures. The lungs belong to, and perform respiration for the whole body.
Decay of the Developmental Organs.
3026. When all the organs are developed, the intestines are drawn together with the vitellus into the abdomen. The chick is still nourished several days after exclusion from the egg by the vitelline mass, which passes through the vitelline canal into the intestine. The vitelline membrane subsequently becomes flaccid, and finally disappears through maceration. In the Mammalia the umbilical vesicle separates at an earlier period from the intestine, and continues to lie in the umbilical cord.
3027. The secernent point of the vitelline membrane or of the umbilical vesicle is the cœcum.
3028. There are therefore two intestinal systems,which branch off in a bifurcated manner from the cœcum, namely, the sexual intestine and the small or truncal intestine.
3029. All embryos have originally umbilical herniæ, which do not originate through protrusion of the intestines out of the abdominal cavity, but through their entrance into the latter being retarded.
3030. The umbilical herniæ therefore indicate an earlier condition of the animal, which has originated through arrest of the development.
3031. At birth all the enveloping membranes die, and their point of liberation is called the navel or umbilicus.
3032. The animal has originated through the umbilicus, and through this has it respired.
3033. All animals which breathe by the anus, do so properly through the navel; animals of this kind are fundamentally umbilical animals.
Parallelism of the Fœtus with the Animal Classes.
3034. During its development the animal passes through all stages of the animal kingdom. The fœtus is a representation of all animal classes in time.
3035. At first it is a simple vesicle, stomach, or vitellus, as in the Infusoria.
3036. Then the vesicle is doubled through the albumen and shell, and obtains an intestine, as in the Corals.
3037. It obtains a vascular system in the vitelline vessels, or absorbents, like as in the Acalephæ.
3038. With the blood-system, liver, and ovarium, the embryo enters the class of bivalved Mollusca.
3039. With the muscular heart, the testicle, and the penis, into the class of Snails.
3040. With the venous and arteriose hearts, and the urinary apparatus, into the class of Cephalopods or Cuttle-fish.
3041. With the absorption of the integument, into the class of Worms.
3042. With the formation of branchial fissures, into the class Crustacea.
3043. With the germination or budding forth of limbs, into the class of Insects.
3044. With the appearance of the osseous system, into the class of Fishes.
3045. With the evolution of muscles, into the class of Reptiles.
3046. With the ingress of respiration through the lungs, into the class of Birds. The fœtus, when born, is actually like them, edentulous.
3047. After birth it is suckled or fed. The milk is the nutrition continued by means of albumen; for the mammæ are verily only the albuminous vessels of the Bird, which are placed free and external in the Mammiferous animal. After the time for sucking is past the young one obtains teeth; and thereby becomes for the first time independent of the mother, and passes over into the class Mammalia. Now, should the sketch here afforded of these parallels be not in all respects correct or justifiable, still sufficient proof remains, that a perfect parallelism is found to take place between the development of the fœtus and that of the animal kingdom.
3048. Animals are only the persistent fœtal stages or conditions of man.
3049. Malformations are only persistent fœtal conditions, or animal formations in individual animal bodies.
3050. Diseases are vital processes in animals. Pathology is the physiology of the animal kingdom. A human fœtus is a whole animal kingdom. (Vid. Oken's 'Die Zeugung,' 'Beyträge zur vergl. Anatomie,' and 'Ueber die Nabelbrüche.')
Periods of Life.
3051. If the young in the ovum or in the mother's body resembles the aquatic animals, and has passed through their organization; so after birth does it belong to the air-breathing animals and traverse their organization.
3052. One period is that of sucking; the edentulous condition of the Bird. This is called the suckling age, baby-hood or infancy.
3053. One is that of the eruption and persistence of the milk-teeth; the condition of the Rodentia, a repetition of the gelatinous animals. This is the age of childhood.
3054. One is the eruption of the permanent set of teeth until the attainment of puberty, or the development of the sexual functions; the condition of the Marsupialia; repetition of the Conchozoa or Shell-animals. This is boyhood.
3055. From the state of puberty until the development of the faculty of understanding; the condition of the Shrews and Bats, the repetition of Insects. The age of youth.
3056. The period of the understanding passes through the Ungulata, and is a repetition of Fishes, Reptiles, and Birds. This is the first stage of manhood.
3057. After the understanding the reason matures; this is the condition of the higher Mammalia up to Man; it is a repetition of the Mammalia. This is adult age or mature manhood.
3058. Then follows the decadence or dying off of the sexual functions; a retrogression through the animal classes. Gray old age.
3059. Finally, the reason and understanding die; childhood returns and terminates with the death of the vegetable in the animal.
3060. Death results through the sexual animal.
3061. Death is only a continuous growth through retrogression into the organic primary matter or Infusoria.
3062. Death is an organized decomposition.
3063. Decomposition is a forming of seeds, ova, and fœtuses.
3064. Dying is a multiplication of self.