382 



THE EVOLUTION OF MAN. 



fluid ; this is the allantois cavity, and it is only after the 

 removal of this membrane that the real embryonic body, 

 which is enclosed in the amnion, is found. 



In Man, the allantois does not attain so great a size, 

 but losing its vesicular form, changes into the placenta 

 soon after it has reached the inner wall of the chorion. 



u.. 



Fig. 137.— Embryo of a Dog, from the right side : a, the first brain- 

 bladder ; l, second ; c, third ; d, fourth ; e, the eye ; /, the ear-vesicle ; gh, 

 first gill-arch {g, lower jaw, h, upper jaw) ; i, second gill-arch ; Urn, heart 

 {k, right auricle ; I, right ventricle ; m, left ventricle) ; n, beginning of the 

 aorta ; o, heart pouch ; p, liver ; q, intestine ; r, yelk-duct ; s, yelk-sac (torn 

 away) ; t, allantois (torn aAvay) : w, amnion ; v, fore-limb ; x, hind-limb. 

 (After Bischoff.) 



Yet even in Man the first rudiment of the allantois is a 

 stalked pear-shaped bladder (Fig. 133, /), just as in other 

 Mammals. I stated this in 1874, in the first and second 



