37$ THE EVOLUTION OF MAN. 



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Fig. 127. 



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 on the fifteenth day, taken from the egg; 

 enlarged : a, yelk-sac ; b, region of 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 

 g3rm (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; b, yelk-sac ; c, lower jaw process 

 of the first gill-arch ; d, upper jaw process of the same ; e, second gill-arch 

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

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



