THE CHORION. 



177 



briefly call the tufted membrane (cJioinon), is completely 

 covered with small knots or tufts, and forms a globe or 

 sphere of 6-8 millimetres in diameter (Figs. 127-129.) In 

 consequence of the accumulation of a large mass of liquid 

 in the inside, the tufted membrane {chorion) continually 

 increases in size, so that the embryo occupies only a small 

 part of the space within the egg-bladder. At the same time 

 the tufts on the chorion increase in number and size, and 



Fig. 132.— Human embryo, with amnion and allantois, in the third week ; 

 with a large globular yelk-sac (below) and a bladder-like allantois (right) ; 

 there are as yet no limbs. The germ and its appendages are surrounded by 

 the tufted membrane {chorion). 



Fig. 133. — Human embryo, with amnion and allantois, in the fourth 

 week. (After Krause.) The amnion {xv) lies pretty close to the body. The 

 greater part of the yelk-sac (d) has been torn away. Behind this the 

 allantois (?) is visible, as a pear-shaped vesicle of considerable size. Arms 

 (/) and legs (6) are just beginning; v, fore-brain; z, twixt-brain; m, 

 mid-brain ; /;, hind-brain ; n, after-brain ; a, eye ; Ic, three gill-arches ; c. 

 heart ; s, tail. 



