No. 535] 



(.EllM-t ELL DETEILMIXAXTS 



shows that only a few of the pole disc granules remain 

 in the egg after the germ cells are formed, as was clearly 

 pointed out in a former paper (Hegner, '09, Plate II, 

 Fig. 16). 



The origin of the pole disc granules is not known. It 

 seemed to me probable that they came from the nucleus 

 of the egg just before maturation and consisted of nuclear 

 material. This conclusion was reached (1) because these 

 granules stain like chromatin, (2) because in many insects 

 the nucleus of the oogonium casts out chromatic material 

 (Nebenkerne), and (3) because the substance which deter- 

 mines the germ cells in Ascaris, Cyclops and Oophthora 

 is of nuclear origin, and in one case (Ascaris) is chro- 

 matin. Wieman believes that "the granules of the pole 

 disc consist of particles derived from the food stream of 

 the ovum that form an accumulation in the protoplasm in 

 its posterior part" (p. 187). This possibility was pointed 

 out in a former paper (Hegner, '09, p. 274), a fact Wie- 

 man seems to have overlooked. It was also suggested 

 in the same place that if the granules are derived from 

 the nurse cells they probably come from the nuclei of 

 these cells. The pole disc granules gradually disappear 

 after the germ cells are formed. 



It may be of interest to mention the results of opera- 

 tions performed upon eggs in which the germ cells had 

 already differentiated at the posterior end (Fig. 5, C). 

 Such eggs, when touched with a hot needle, continued to 

 develop, and produced embryos and larvse without germ 

 glands. This I believe is the earliest stage on record on 

 which surgical castration has been performed. 



The visible presence of germ cell determinants in the 

 primordial germ cells of the animals described above sug- 

 gests two possibilities as to their importance: (1) They 

 may represent idiochromatin, *. e., germ plasm, or (2) 

 they may influence the metabolism of the cells and thus 

 determine their character. 



1. The history of the germ cells in chrysomelid beetles 

 illustrates in a 'remarkable way the theory of germinal 

 continuity as expressed by Weismann ( '04). Weismann 

 believes with Nageli that "there are two great categories 



