288 Rolx3rt Wilhelm Hegner. 



not a cell will become a genu-cell depends on its position in the egg 

 just previous to the formation of the blastoderm. The cleavage 

 nuclei of the beetle's eggs are not separated by cell boundaries, as 

 are those of several other animals (e. g. Cyclops and Ascaris), where 

 an earlier differentiation of the primordial germ-cells takes place, 

 but are intimately connected by the cytoplasm which is present 

 throughout the egg in the interdeutoplasmic spaces. We have thus 

 a syncytium in which the nuclei are widely separated from one 

 another by the enormous mass of yolk. The various substances 

 (e. g., the granules of the pole-disc) are, therefore, less easily seg- 

 regated into a single cell in the egg of Calligrapha than are similar 

 structures (e. g., the '^Aussenkornchen" of Cyclops, Hacker, 189Y) 

 in alecithal eggs. This fact may account for the relatively late 

 stage at which the primitive germ-cells of Calligrapha and allied 

 forms can be recognized as such. 



V. Summary. 



1. A layer of dark-staining granules, the pole-disc, is present 

 at the posterior end of the eggs of Calligrapha and Leptinotarsa 

 before fertilization takes place; this layer is later intimately as- 

 sociated with the development of the pole-cells. 



2. The genesis of the pole-cells is as follows: (1) four nuclei 

 lying near the posterior end of the egg are recognized by their posi- 

 tion as pole-cell antecedents (Figs. 5 and 12) ; (2) these four nuclei 

 divide producing eight daughter nuclei which move closer to the 

 periphery of the egg (Fig. 7) ; (3) these in turn divide resulting 

 in sixteen nuclei, arranged in pairs, each of which separates en- 

 tirely from the egg, carrying with it a portion of the ''Keimhaut- 

 blastem" containing pole-disc granules (Figs, lo and 19-22) ; (4) the 

 sixteen primary pole-cells divide to form thirty-two secondary pole- 

 cells (Fig. 14) ; these divide resulting in sixty-four tertiary pole- 

 cells (Figs. 15-16) which do not increase in number until a late 

 period of embryonic life (Fig. 45) ; (5) in mitosis the pole-disc 

 granules are, approximately, equally distributed between the two 

 daughter cells (Figs. 17 and 27 a). 



