THE BREEDINC, HABITS OF ANIMALS 



197 



ence as larva? or adults, but not nourished by the mother. Ovovi- 

 viparous species. 



Fig. 150. — Embryo sharks of a ^•ivipa^ous species, M^inidus mustelus (Linnaeus), 

 attached to the wall of the uterus, which is here dissected open. The expanded end of 

 each umbilical cord forms a placenta, as in the mammals, and the young receive nourish- 

 ment through it from the mother. (Aftir Fowler.) 



(b) Eggs retained and the embryo nourished by the mother. True 

 viviparous species. 



No Evolutionary Sequence. — It will l)e seen from the examples given 

 above that just as there is no general evolutionary sequence in the methods 



