MUSEUM OF COMPARATIVE ZOOLOGY. 199 



pole, — the so-called polar globule. The steps in its formation have 

 already been followed in the living egg, in so far, at least, as concerns 

 the successive phases of its changing outline. 



The slight annular depression marking the limit of the external aster 

 in the previous stage gradually deepens, and the transparent fibrous 

 protoplasm of the outer star, together with a portion of the more 

 granular protoplasm in its immediate vicinity, is pinched off by this 

 deepening constriction. 



The internal alterations accompanying this process (Figs. 40-42) 

 are in a measure only the continuation of those noticed in the last stage. 

 The maturation figure has migrated farther from its central position. 

 The external star has undergone a more thorough metamorphosis than 

 the deeper one. The spindle has suffered a constriction at its equator, 

 but its length remains nearly unaltered. 



What is left of the radial structure of the outer star is discoverable 

 within the polar globule. A few faint lines, lying mostly near its sur- 

 fiice, are all that can now be seen ; even these are not uniformly observ- 

 able. When present, they are often so closely applied to the surface of 

 the polar globule as to leave the observer for a time in doubt if he has 

 not before him a series of striations or foldings in the envelope of the 

 globule. The slightly serrated outline of that portion of the globule 

 which in Fig. 41 faces the vitellus, seems at first to strengthen the lat- 

 ter opinion ; but a careful inspection seldom fails to show that the mark- 

 ings are not all parallel, — that different systems cross at a slight angle, 

 which could hardly be expected of surface foldings. The greater part 

 of the contents of the polar globule show not the least trace of such 

 a structure, but are simply either quite transparent and homogeneous, 

 or show a very fine punctate appearance, in which a few larger granules 

 are occasionally found. The structure of the central portion will receive 

 attention a little further on. The body which formed the centre of 

 radiation is usually no longer distinguishable, its substance possibly hav- 

 ing become disseminated in the globule. Occasionally, however, (comp. 

 Fig. 63,) one discovers, attached to the free pole of the globule and pro- 

 jecting inward, a prominent thickening {aa'1) which I am inclined to 

 consider as at least a portion of this refractive corpuscle w^hich has by 

 this time gained an intimate connection with the envelope of the globule. 



The deeper star, having moved further from the centre of the yolk, as 

 already indicated, is now tangent to the inner surface of the vitelline 

 sphere. The amount of substance that is brought directly within the 

 influence of this star is slightly increased, principally on the side opposite 



