EFFECTS OF REMOVING GERM-CELLS. 21 



number) that come in contact with the granules of the pole-disc, 

 do not remain in the " Kleimhautblastem " and later become the 

 centers of blastoderm cells as do the other nuclei but become 

 completely surrounded by a thin layer of these darkly stain- 

 ing bodies and continue their migration until they are entirely 

 separated from the egg. They then lie between the vitelline 

 membrane and the blastoderm in a closely packed group (Fig. 

 2). Each of these sixteen cells ("pole-cells") has the appear- 

 ance of the one shown in Fig. 3. They soon divide by mitosis 

 to form thirty-two. During this division the pole-disc granules 

 are equally distributed among the daughter cells. Another 

 division increases the number to sixty-four. This number is 

 reached at the end of twenty-four hours and no further divisions 

 take place until about the time of hatching. The blastoderm 

 cells increase rapidly in number and can be distinguished from 

 the cells just described not only because of the absence of granules 

 but also by the smaller size of their nuclei. No difficulty was 

 experienced in tracing the sixty-four cells containing pole-disc 

 granules until they became the definite germ-gland. 



These phenomena give reasonable grounds for the following 

 conclusions. All the cleavage nuclei in the eggs of the above 

 named beetles are potentially alike until in their migration toward 

 the periphery they reach the " Keimhautblastem." Then those 

 which chance to encounter the granules of the pole-disc are dif- 

 ferentiated by their environment, /. e., the granules, into germ- 

 cells ; all the other cleavage products become somatic cells. 

 The granules of the pole-disc are therefore either the germ-cell 

 determinants or the visible sign of the germ-cell determinants. 

 The term determinant is not used here in the Weismannian sense 

 but simply is meant to describe the material which fixes the 

 character of the cells. 



At first an attempt was made to tie off the posterior end of 

 freshly laid eggs by means of fine silk thread in order to remove 

 the pole-disc. This proved impossible for in every case the pres- 

 sure burst the chorion. It was later found that if the chorion is 

 punctured with a needle at any point a small drop of the contents 

 is forced out by the turgidity of the egg and can be removed 

 with filter paper. The eggs of these insects are perfectly oriented 



