THE POLE DISC OF CHRYSOMELID EGGS. 



H. L. WIEMAN, 

 University of Cincinnati. 



Hegner (09^^)^ has described a disc-shaped mass of darkly stain- 

 ing granules at the posterior end of freshly laid eggs of two 

 genera of beetles, Calligrapha arid Leptinotarsa. In earlier publica- 

 cations (Hegner, 08, 0(^df these granules are spoken of as " germ 

 cell determinants" in the sense that they fix the character of the 

 sex cells. The use of the word determinant is open to criticism 

 inasmuch as the term implies the attribute of certain potentialities 

 that these granules have not been shown to possess. In the 

 complete account of the early history of the germ cells (Hegner, 

 09^)^ the word deteinninant does not appear, and the conclusion 

 regarding their significance is summed up in the statement, that 

 the "pole-disc" is " intimately associated with the development 

 of the pole cells" (p. 288). 



In view of the experiments of Lyon, Lillie, Morgan and others, 

 which center about the question of the role of preformed mater- 

 ials in the ^^% as versus a predetermined method of action as the 

 essential factor in embryonic development, it is important to know 

 something of the nature and origin of the granules of the pole 

 disc. The data derived from the experiments of these investiga- 

 tors tend to indicate that early developmental phenomena can 

 take place even though the original configuration of the ground 

 substance be radically changed. The formative processes do not 

 depend on the materials displaced by centrifuging, but are bound 

 up in the organization of the ground substance of the egg 

 protoplasm. 



Hegner did not determine the origin of the pole disc, but is 

 inclined to believe that it is composed of particles of chromatin 

 derived from the nucleus. No expulsion of material from the 

 nucleus was actually observed ; the conclusion being based 



'^ Journal of Morphology , XX., 2, 1909. 



^Biological Bulletin, XVI., i, 1908 ; Journ. Exp. Zool., VI., 4, 1909. 



