II DEVELOPMENT OF MAN 89 



differences between them are inconsiderable, while, 

 in their subsequent course they diverge more and 

 more widely from one another. And it is a general 

 law, that, the more closely any animals resemble 

 one another in adult structure, the longer and the 

 more intimately do their embryos resemble one 

 another : so that, for example, the embryos of a 

 Snake and of a Lizard remain like one another 

 longer than do those of a Snake and of a Bird ; 

 and the embryo of a Dog and of a Cat remain like 

 one another for a far longer period than do those 

 of a Dog and a Bird ; or of a Dog and an Opossum ; 

 or even than those of a Dog and a Monkey. 



Thus the study of development affords a clear 

 test of closeness of structural affinity, and one 

 turns with impatience to inquire what results are 

 yielded by the study of the development of Man. 

 Is he something apart ? Does he originate in a 

 totally different way from Dog, Bird, Frog, and 

 Fish, thus justifying those who assert him to have 

 no place in nature and no real affinity with the 

 lower world of animal life ? Or does he originate 

 in a similar germ, pass through the same slow and 

 gradually progressive modifications, depend on 

 the same contrivances for protection and nutrition, 

 and finally enter the world by the help of the same 

 mechanism? The reply is not doubtful for a 

 moment, and has not been doubtful any time these 

 thirty years. Without question, the mode of origin 

 and the early stages of the development of man are 



