28 Dynamic Theory. 



At this stage of human development the embryo is in all essential 

 particulars the counterpart of the embryos of all the higher mammals. 

 Some of the parts may differ in relative size, but the corresponding es- 

 sential parts are present in all, and it would require an expert to tell the 

 difference between the human embryo of four weeks and that of a 

 horse, ox, dog or rabbit at its corresponding stage of development. If 



Fish. 



Chick. 



Hog. 



Man. 



FiGS. 33, 34, 35, 36, top row, represent the embryos of fish, chick, hog, and man, at an 

 early age. 



FIGS. 37, 38, 39, 40. Same at a more advanced period, after formation of limbs and 

 brain bladders, &c., has begnn. 



FIGS. 41, 42, 43, 44. A still more advanced as.ro, in which gill openings are lost (except 

 in the fish) and the limbs more developed. The figures are magnified, the top ones the 

 most. The allantois, yelk sac and amnion are left off. Letters the same in all. 

 v. Fore-brain. r. Spinal marrow. 



>. Vertebral column. 



ra.-Mid 

 A.-Hind 

 n. After 



a. Eye. 

 o. Ear. 

 g. Heart. 



{.Fore limbs. 

 .-Hind " 

 s. Tail. 

 A;. Gill arches. 

 (After Hxckel.) 



