Chap, iv.] 



OP ANIHAL GENERATION. 



829 



A very impoi-tant general .fact, of which the partisans of the 

 evolutive or Darwinian doctrines make great use, and with 

 justice, is the identity of the embryonary forms at the outset 

 in all the vertebrates, and the appearance in a regular and 



Fia. 61. 



Ovnm of dog. The embryon in form of 



shoe sole is outlined. 

 a, dorsal fissure ; 

 i, dorsal plates ; 



c, clear area ; 



d, opaque germinatiTe area ; 



e, membrane of the genninative vesicl^. 

 The small superior figure is of natural size. 



The inferior figure is magnified. 



Pio. 62. 



Embryon of a dog's ovum, twenty days old. 

 Dorsal fissure widely open and surrounded 

 everywhere with a bright edge, which indi- 

 cates the first deposit of the nervous sub- 

 stance on the depth and the walls of the 

 fissure. In the depth is seen on the median 

 line the clwrda dorsaUs represented by a 

 darker stripe. — a, 6, c, rudiments of the cere- 

 bral vesicles ; e, posterior rhomboidal smus ; 

 i, body of primordial vertebrae ; /, lateral 

 plates ; g, middle and external ve^ments of 

 the blastodermic vesicle, still united; h, 

 mucous vestment; i, body of the embryoii. 



successive order of the characteristics of each type. We may 

 compare the embryons of the vertebrates to a group of travellers 

 starting from the same place, and entering first of all a vast 

 general route, which they forsake to enter roads of more and more 

 secondary importance, and diverging less and less. It is first of 



