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.