348 



REPRODUCTION 



were, into the substance of the blastoderm, and while the 

 body cavity is being formed, the layers of the somatopleure 

 grow up over the embryo to meet and blend dorsally. (Figs. 

 107, 108.) The two layers of which the somatopleure is 

 composed separate, the outer forming the false amnion and 



FIG. 104. Diagram of 

 fecundated egg. 



a, umbilical vesicle; b, 

 amniotic cavity; c, allan- 

 tois. (Kirkes after Dai- 

 ton.) 



FIG. 105. Fecundated egg with allantois 

 nearly complete. 



a, inner layer of amniotic fold; b, outer layer of 

 ditto; c, point where the amniotic folds come in 

 contact. The allantois is seen penetrating between 

 the outer and inner layers of the amniotic folds. 

 This figure, which represents only the amniotic 

 folds and the parts within them, should be compared 

 with Figs. 99, 100, in which will be found the struc- 

 tures external to these folds. (Kirkes after Dalton.) 



the inner the true amnion. The false amnion now coalesces 

 with the original vitelline membrane to constitute the false 

 chorion. Evidently there is thus formed a closed cavity, the 

 amniotic cavity, between the true amnion and the body of 

 the embryo. 



At first the amnion and the embryo are in close contact, 

 but soon the cavity begins to be distended with the fluid, the 

 liquor amnii, which increases until it reaches a considerable 

 quantity. It affords mechanical protection to the fetus dur- 

 ing intrauterine life, and at labor serves to evenly dilate the 

 cervix. When this has been accomplished is the usual time 

 at which the sac ruptures and the liquor amnii escapes. It 

 also supplies the fetal tissues with water, parts of it being 

 swallowed from time to time. 



