18 



DEVELOPMENT OF THE FROG'S EGG 



[Ch. ir 



to one pole of the spindle, and half to the other. The spindle 

 has assumed, during this time, a radial position with respect to 

 the egg, so that we may speak of a distal and of a proximal or 

 central end (Fig. 11, A). The distal end pushes out into a 

 protrusion of protoplasm that has simultaneously formed at this 



«** 



Fig. 11. — Extrusion of first polar body and fertilization of egg of Toad. (Fi ni 

 preparations made by Helen D. King.) A. First polar spindle. B. First polar 

 body extruded; second polar spindle present. C. Entrance of spermatozoon. 

 D. Male and female pronuclei. E. Apposition of two pronuclei. F. First seg- 

 mentation-spindle. 



point of the surface of the egg. This protrusion of protoplasm 

 with its enclosed half of the nucleus gradually pinches off from 

 the surface of the egg, and there is thus formed the first polar 

 body (Fig. 11, B). The egg gets a thin layer of gelatinous 



