No. 611] GENESIS OF ORGANIZATION OF INSECT EGG 659 



tinguished from the nurse cells by the presence of a pe- 

 culiar ring of nuclear material within the cytoplasm and 

 by their larger size. The gyrinid beetle, Dineutes nigrior 

 (Fig. 9), resembles Dytiscus in general, but the ultimate 

 oogonium passes through one less division, thus giving 

 rise to one oocyte and only seven nurse cells.^* The im- 

 portant fact is that during these differential divisions, in 

 both cases, the nurse cells, which may be considered so- 

 matic since they are unable to reproduce, are deprived of 

 part of their nuclear material. Apparently they differ 

 from their sister cell, the oocyte, in this one respect, and 

 it is therefore the presence of this nuclear material that 

 makes it possible for the oocyte to develop into a new in- 

 dividual. This is one of the most striking cases of the 

 passage of large masses of nuclear material into the cyto- 

 plasm. No such differential divisions have been discov- 

 ered in chrysomelid beetles nor in the other insects where 

 the nurse cells arise from oogonia, but they may occur in 

 some way that has not been revealed by our methods of 

 research. 



The writer has discussed this subject rather fully with 

 relation to the origin of nurse cells and oocytes in the 

 honeybee.2^ In this insect a single oogonium gives rise 

 to a rosette-like group of cells that are connected with 

 one another by strands— probably of a mitochondrial na- 

 ture—the remains of preceding mitotic divisions. There 

 is no visible difference among the cells in a rosette which 

 are hence apparently potentially alike. Nevertheless one 

 or several from each rosette enlarge to form oocytes 

 which are nourished by the r^st acting as nurse cells. 

 What determines the differentiation of certain cells into 

 oocytes is not known but the following hypotheses have 

 been expressed. 



i^IIegner and Russell, Wm, Proc. Xat. Acad. Sv., Vol. 2. 

 25 Hegner, 1915, Journ. Morph., Vol. 26. 



