Germ-Cells in Clii*ysomelid Beetles. 263 



needs since most of the peripheral layer has already been carried 

 away by the nuclei that first reach the surface. One of these delayed 

 nuclei (Fig. 22, a) shows, embedded in its accompanying cyto- 

 plasm, a number of small yolk-globules which have not yet been 

 dissolved. 



I have already said that eight pairs of pole-cells protrude from 

 the posterior end of the egg and from a single layer there (Fig. 13) ; 

 these I shall speak of as the primary pole-cells. It has also been 

 shown that when these sixteen primary pole-cells have become com- 

 pletely separated from the egg they are in the prophases of mitosis 

 (Fig. 22). These now undergo their first division, giving rise to the 

 secondary pole-cells which immediately divide again. However, 

 before this second division is completed an accurate count of the 

 number of pole-cells is possible as the presence of granules easily 

 distinguishes them from those of the blastoderm. The number of 

 pole-cells ranges from thirty-two to forty at this stage, thirty-four 

 being present in the specimen illustrated (Fig. 14) ; only one of 

 these is dividing (Fig. 17) showing that mitosis does not occur in 

 all at the same time. A longitudinal section through an egg taken 

 from the same batch as that just described also shows one pole-cell 

 in a similar condition (Fig. 23, a). We conclude from this that 

 the sixteen primary pole-cells have divided, resulting in thirty-two, 

 and that two of these secondary pole-cells have produced daughter 

 cells, thus- bringing the total number to thirty-four. During the 

 division of the pole-cells (Fig. 17) all of the granules separate into 

 two approximately equal groups, which form a thin layer closely 

 applied to the cell boundary at either end. 



The pole-cells just previous to their second and final division, 

 can, as already mentioned, be distinguished from the adjacent blasto^ 

 derm-cells by the presence within the cytoplasm of the dark-staining 

 granules of the pole-disc ; they also at this stage show a difference 

 in the structure of their nuclei. One cell of each kind, pole and 

 blastoderm, is shown highly magnified in Fig. 28. Here we see 

 that the nucleus of the pole-cell (p.c) is the larger; it contains a 

 relatively few rod-like pieces of chromatin which are most abundant 

 near the nuclear membrane. In contrast to this, the smaller nucleus 



