240 Records of the Indian Museum. {Wot,. XVI, 191 9.] 



with the development of the placenta by the modification of the 

 yolk-sac, nourishment is obtained directly from the blood of the 

 mother through the blood-vascular system. In some cases addi- 

 tional structures or appendicula are developed on the placental 

 cord, and these probably absorb the secretion of the uterine wall 

 in which the embryos are floating. 



II. In the aplacental forms the yolk-sac persists as such 

 through a greater part of the embryonic life and the yolk in it is 

 directly taken into the alimentary canal with or without the inter- 

 mediation of an internal yolk-sac ; possibly, as has been suggested, 

 the branchial filaments also help in its absorption. In the earlier 

 stages, when the branchial filaments are present, these help in the 

 absorption of the secretion of the uterine glands. The blood 

 vessels in the mesoblastic portion of the yolk-sac are also of use 

 in absorbing the nourishment contained within it. During the 

 later stages of development special processes are developed in 

 some cases from the maternal uterine wall and these processes or 

 trophonemta, entering the embryonic spiracles directly, pour the 

 secretion into the pharynx of the embryo. It may also be men- 

 tioned here that during the embryonic portion of the life history 

 the stomach does not function as such, but merely acts as a channel 

 for the transport of food to the colon, where absorption mostly 

 takes place. 



