1876.) A Remarkable Life History and its Meaning. 651 
bryo into two portions, of which the one nearest the blood chan- 
nel of the nurse becomes developed into a true placenta (Figure 
56, 12), similar, in function as well as in structure, to that of a 
Fic. 56. Embryo of solitary Salpa. 
fetal mammal, while that portion which is directed towards the 
breathing chamber becomes developed into the embryo proper. 
This is nourished with the blood of the nurse by means of the 
Fie. 57. Embryo more advanced, and ready to be discharged. 
Placenta, and grows very rapidly and soon assumes the par 
teristics of the solitary form. In Figure 57 an embryo is figu 
_ ® it appears when development is very much advanced. It is 
