376 



THE EVOLUTION OF MAN. 



Fig. 127. 



IIP 



Fig. 128. 



Fig. 130. 



Fig. 131. 



Fig. 127- — Human egg between the twelfth and thirteenth day. After 

 Allen Thomson. 1. Not opened ; natural size. 2. Opened, and enlarged. 

 Within the outer tufted membrane (chorion) the small curved germ lies upon 

 the left of the upper side of the large intestinal germ. vesicle. 



Fig. 128. — Human egg on the fifteenth day. After Allen Thomson. 

 Natural size, and opened. The small germ lies in the upper right-hand part 

 of the right half. 



Fig. 129. — Human germ oo the fifteenth day, taken from the egg; 

 enlarged : a, yelk-sac ; b, region ot the neck (where the medullary furrow is 

 already closed) ; c, head part (with open medullary furrow) ; d, hind part 

 (with open medullary furrow) ; e, a shred of the amnion. 



Fig. 130. — Human egg between the twentieth and twenty-second day. 

 After Allen Thomson. Natural size ; opened. The outer tufted membrane 

 (chorion) forms a capacious vesicle, to the inner wall of which the small 

 germ (above, on the right) is attached by a short navel-cord. . 



Fig. 131. — Human germ between the twentieth and twenty-second day, 

 taken out of the egg; enlarged : a, amnion ; ?>. yelk-sac ; c, lower jaw process 

 of the urst gill-arch; d, upper jaw process ot' the same; e, second gill-arch 

 (behind it are two other small arches). Three gill-openings are very plainly 

 seen j /, rudiments of the fore-limbs ; g, ear-vesicle ; h, eye ; i, heart. 



