REPRODUCTIOK. 



81 



<^.. 



Fig. 82.— Diagram of an embryo showing the relations of the vascular allantois to the 

 villi of the chorion (Cadiat). e, enibryo lying in the cavity of the amnion; ys, 

 yelk-sac^ a/, allantois; A. F, allantoic vessels dipping into the villi of the chorion; 

 ch, chorion. 



In the mare especially these parts can be readily distin- 

 guished. From the connection of the portion that ultimately 

 forms the bladder with the 

 main sac, as indicated 

 above, there is ground for 

 regarding the allantoic 

 fluid in the later stages of 

 gestation, at all events, as 

 a sort of urine. 



This fluid is at an ear- 

 ly period abundant and 

 colorless, later yellowish, 

 and finally brown. Since 

 at one time it contains 

 albumen and sugar, it 

 may serve some purpose 

 in the nutrition of the 

 foetus. 



When most suggestive 

 of urine in the latest stages 

 of gestation, it contains 

 6 



Fia. 83.— Diagram of the foetal membranes of 

 the Virginian opossum (Haddon, after Os- 

 bom). Two villi are shown greatly enlarged. 

 The processes of the cells, which have been 

 exaggerated, doubtless correspond to the 

 pseudopodia described by Caldwell, al, 

 allantois ; am, amnion; s. t, sinus termi- 

 nalis; s.z, subzonal membrane; v, villi on 

 the subzonal membrane in the region of 

 the yelk-sac ; ys, yelk-sac. The vascular 

 splanchnopleure (tm>oblast and mesoblast) 

 is indicated by the black line. 



