238 



ROBERT W. HEGNER. 



khbh 



C. bigsbyana, C. hmata and Leptinotarsa decemlineata. 1 Before 

 the results of those experiments and the data contained in the 



present contribution can be 

 understood clearly, a brief 

 account of the structure of 

 freshly laid chrysomelid 

 eggs and of the principal 

 stages in their normal em- 

 bryonic development is 

 necessary. 



The freshly laid egg (Fig. 

 i) consists of a large central 

 \ -gn. mass of yolk globules (y) 

 and a comparatively thin 

 superficial layer of cyto- 

 plasm, the " Keimhaut- 

 blastem " (khbl). Two en- 

 velopes cover the egg, the 

 vitelline membrane (vm) 

 and the chorion. Polar 

 bodies are usually present 

 at this time, and the egg 

 nucleus is in the act of 

 union with the sperm nu- 

 cleus (gn), or else cleavage 

 has already begun. Em- 

 bedded in the "Keimhaut- 

 blastem" at the posterior 

 end of the egg is a disc- 

 shaped mass of darkly 

 staining granules, which I 

 have called the pole-disc, 

 or germ cell determinants 

 (gcd}. 



FIG. i. A longitu inal section through 

 an egg of Calligrapha c. tgsbyana four hours 

 after deposition. gcd, germ cell determi- 

 nants; gn, germ nuclei copulating; khbl, 

 " Keimhautblastem "; p, posterior; vm, vitel- 

 line membrane; y, yolk. The eggs of Lep- 

 tinotarsa decemlineata are not visibly different 

 from those of C. bigsbyana. 



As cleavage progresses, 

 a separation of the cleavage products into sections occurs; the 



iHegner, R. W., 'o8b, "The Effects of Removing the Germ Cell Determinants 

 from the Eggs of Some Chrysomelid Beetles," BIOL. BULL., Vol. 16 



