STUDIES ON GEEM CELLS 417 



oogonia; the epithelial cells are of mesodermal origin. As noted 

 above, the investigations of Giardina ('01) and many others 

 upon the genesis of the nm^se cells in the ovaries of insects have 

 established the fact that in some species a single oocyte and a 

 definite number of nurse cells arise from a single ultimate oogo- 

 nium. Wieman ('10b) has followed the history of the oogonia in 

 Leptinotarsa signaticoUis through the larval and adult stages, 

 but was unable to find any evidence that the nuclei inaugurate 

 differentiation as in Dytiscus (Giardina, '01; et al.). He con- 

 cludes that "the process seems to be the result of several distinct 

 cell elements which operate together as a whole" (p. 148) and 

 that the semi-fluid matrix which results from the liquefaction 

 of cells at the base of the terminal chamber may exert a "specific 

 effect on those germ cells coming under its influence, enabling 

 them to develop into ova, while the more distant germ cells be- 

 come nurse cells" (p. 147). My observations agree with those 

 of Wieman; no definite mmierical relations nor nuclear evidence 

 were discovered during the differentiation of the oogonia into 

 oocytes and nurse cells. The data available do not suggest 

 any method of differentiation not already proposed, and still 

 leave the question whether the nurse cells should be regarded as 

 abortive germ cells or true somatic cells, one of personal opinion. 

 (2) The origin of the pole-disc granules in Leptinotarsa decem- 

 lineata. The pole-disc in Chrysomelid eggs has already been 

 described and figured, and comparisons with similar structures 

 in the eggs of other animals will be made later (p. 461). Pre- 

 vious to the publication of my results ('08, '09) no granules re- 

 sembling those of the pole-disc had been discovered in the eggs 

 of Chrysomehd beetles, although Wheeler ('89), Lecaillon ('98) 

 and others had studied various species belonging to this family. 

 Wieman ('10a) has attempted to determine the origin of these 

 granules, using the germ cells of Leptinotarsa signaticoUis for 

 this purpose. His conclusion, which was arrived at from cir- 

 cumstantial evidence, is "that the granules of the pole-disc 

 consist of particles derived from the food stream of the ovimi 

 that form an accumulation in the protoplasm in its posterior 

 part" (p. 187). In a previous paper (Hegner, '09a) I have 



