OBSERVATIONS ON THE MATURATION PROCESSES. 43 



perhaps it arises in divided first polar cells during the cleavage stages of 

 the egg. 



Although the cytoplasm of the polar cell has not been studied care- 

 fully by us, its general features are as follows. In the newly formed 

 polar cell the more distal part of the cytoplasm appears very clear (figs. 

 18, 19). Later, it is of uniform appearance throughout the cell, and in 

 some cases is apparently like that of the egg ; but more often it is either 

 more granular or more homogeneous and clear than the egg cytoplasm. 

 In the smaller polar cells it has the latter structure and it sometimes 

 shows what appear to be ill-defined vacuoles (fig. 36). The interzonal 

 filaments within the polar cell are, at first, very evident (figs. 18, 19). In 

 time they lose their connection with the cell plate (figs. 19 and 31a), which 

 then quickly disappears. Occasionally there can be observed in the polar 

 cell fibers which are parallel with one another ; but it is uncertain whether 

 they are the remains of interzonal filaments or fibers of an abortive 

 spindle. 



It may be inferred from the amitotic (or imperfect mitotic) division 

 of the chromatin that the whole polar cell is capable of division. Such, 

 indeed, is the case, for, previous to the formation of the second polar 

 cell, the first polar cell may be observed in many instances to be divid- 

 ing into two or more parts, as shown in figs. 32 and 33, or to be simply 

 constricted (fig. 31a). Less frequently the small polar cell is seen to be 

 already divided into two parts. This dividing of the polar cell doubt- 

 less aids in its rapid degeneration by increasing the external surface 

 exposed to the action of absorption. 



The polar cell quickly loses its connection with the egg, because the 

 interzonal filaments become severed from the cell plate. This separa- 

 tion is evident as early as the time of ovulation and may be aided by 

 that process, as described on page 22 and shown in figs. 31a and 316, 38, 

 39, and 40 (figs. 31a and 316 being enlarged views of sections of the egg 

 and polar cell of which fig. 40 shows another section) . In the egg illus- 

 trated in figs. 31a and 316 the polar cell is separated from the egg and 

 probably from the cell plate, which is seen in fig. 316. (In this case, 

 however, the existence of the cell plate is a little doubtful.) The evi- 

 dence leads to the belief that the first polar cell need not remain at the 

 place where it was formed, but may, according to circumstances, change 

 its position under the zona, even to such an extent as to come to lie 

 diametrically opposite the point of its origin. The bearing of these 

 observations on the question of the relative positions of the first polar 

 cell and the second spindle will be considered later (p. 63). The first 

 polar cell usually lies in a depression in the surface of the egg. 



