ORIGIN OF SPECIES 221 



confirming an older observation of Roux. When, 

 however, Morgan put the egg upside down after the 

 destruction of one of the first two cells, and com- 

 pressed the eggs between two glass plates, the sur- 

 viving half of the egg gave rise to a perfect embryo of 

 half-size (and not to a half-embryo of normal size 

 as before)."^^ 



The interest that attaches to these monstrosities 

 produced by experimental embryology, has been 

 largely due to the fact that normally one egg gives 

 rise to only one individual. However, these experi- 

 ments are of extreme interest to my theory. 



Concerning man: Necessarily, most of the facts 

 known about the details of the process of fertilization 

 have been gained through observation of, and ex- 

 perimentation with, lowly organisms. However, the 

 human ovum and spermatozoon are structurally built 

 on the same lines as the ova and spermatozoa of the 

 animals which have been the subject of elaborate 

 experiments. The human ovum (about 1/120 inch 

 in diameter) is imbedded in the Graafian follicle, a 

 vesicle about as large as a pinhead. Periodically an 

 ovum ripens in one or the other of the two ovaries, 

 and is then discharged from the ovary and carried 

 to the uterus. Here, in the event of impregnation, 



^ The Mechanistic Conception of Life, 216. 



