CHAPTER IV. 

 OUR EMBRYONIC DEVELOPMENT. 



The older embryology. The theory of preformation. The theory 

 of scatulation. Haller and Leibnitz. The theory of epigenesis. 

 C. F. Wolff. The theory of germinal layers. Carl Ernest Baer. 

 Discovery of the human ovum. Kemak, Kolliker. The egg-cell 

 and the sperm-cell. The theory of the gastreea. Protozoa and 

 metazoa. The ova and the spermatozoa. Oscar Hertwig. Con- 

 ception. Embryonic development in man. Uniformity of the 

 vertebrate embryo. The germinal membranes in man. The 

 amnion, the serolemma, and the allantois. The formation of the 

 placenta and the " after birth." The tlecidua and the funiculus 

 umbilicalis. The discoid placenta of man and the ape. 



Comparative ontogeny, or the science of the develop- 

 ment of the individual animal, is a child of the 

 nineteenth century in even a truer sense than com- 

 parative anatomy and physiology. How is the child 

 formed in the mother's womb ? How do animals 

 evolve from ova ? How does the plant come forth 

 from the seed ? These pregnant questions have 

 occupied the thoughtful mind for thousands of years. 

 Yet it is only seventy years since the embryologist 

 Baer pointed out the correct means and methods for 

 penetrating into the mysteries of embryonic life ; it is 

 only forty years since Darwin, by his reform of the 

 theory of descent, gave us the key which should open 

 the long-closed door, and lead to a knowledge of 

 embryonic agencies. As I have endeavoured to give 

 a complete, popular presentation of this very interest- 

 ing but difficult study in the first section of my 

 Anthropogeny, I shall confine myself here to a brief 



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