MAMMALIA. 



305 



eye-muscles do not differ widely from the condition found in the 

 frog (p. 221). But the sclerotic is not supported by cartilage, 

 and the lens is much flatter (as in Fig. 63). The accessory 

 structures, besides muscles, are the conjunctiva, three eyelids, and 

 lachrymal and Harderian glands. 



cnt. 



Fig. 92. FORMATION OF BLAS- 



TOCYST IN THE RABBIT (after 



E. Van Beneden).a, Bias- 

 tula ; 6, e, d, successive stages 

 in the formation of the blas- 

 tocyst; ect, outer cells; ent, 

 inner cells ; z.p, zona pel- 

 lucida. 



DEVELOPMENT. 



1. Early Stages. Cleavage (segmentation) (Fig. 92) is com- 

 plete and almost regular, there being only a very small quantity 

 of food-yolk in the minute oosperm to impede it. By successive 

 bipartitions eight cells are produced, four of which are larger 

 than the others, and are called outer cells, from their subsequent 



UNIVEBSITT 



V. of 



