Germ-Cells in Chrysomelid Beetles. 257 



III. Observations. 

 1. The Pole Disc. 



A disc-shaped mass of dark staining granules is present at the 

 posterior end of the freshly laid eggs of both Calligrapha and Lep- 

 tinotarsa; these granules lie suspended in the inner stratum of the 

 "Keimhautblastcm." This layer of granules, which I shall call the 

 pole-disc, plays one of the most important roles in the genesis of the 

 pole-cells ; on this account I shall in this place describe its early 

 characteristics, leaving its later history to the succeeding chapter. 



Unfortunately, material was not at hand with which to trace the 

 origin of this pole-disc, the earliest stage in my preparation (Fig. 

 2) l>eing the eggs of Leptinotarsa taken from the oviduct just before 

 deposition. At this time the pole-disc is present in the position it 

 occupies throughout the entire course of the early cleavage of the egg. 

 Under low magnification it appears in longitudinal sections as a dark 

 irregular line lying just within the surface at the posterior end of 

 the egg; under high powers, however, it is seen to be granular in 

 structure. In the section figured (Fig. 2) it occupies the innermost 

 portion of the "Keimhautblastem ;" its granules are grouped together 

 in small masses giving the entire pole-disc the appearance of a broken 

 strand. These granules are easily distinguished from the cytoplasm 

 in which they are suspended, by their large size and susceptibility 

 to various stains ; they appear to be arranged around small vacuoles 

 which vary in size in the different preparations examined, irrespec- 

 tive of the age of the egg. Thus the granules in the pole-disc under 

 consideration (Fig. 2) are crowded as closely together as they ever 

 become, while in other eggs taken from the same batch they were 

 widely separated. 



Fig. 1 represents the posterior end of an egg of Calligrapha; here 

 we see that the pole-disc occupies about one-eighth of the total area. 

 The central part of the disc is denser than it is in any other region 

 of it except the periphery, where an irregular margin is produced 

 by numerous dark projections. Longitudinal sections of the pole- 

 disc (Fig. 3) explain this difference in density, as it is found to 

 be thickest in the center, and to be thrown into irregular folds at 



