Germ Cells of Leptinotarsa Signaticollis. 139 



During the next decade or more, most investigators were oc- 

 cupied with the study of the structure and development of the 

 various envelopes of the egg and ovary, but in 1864, Claus, re- 

 turning to the question of the origin and significance of the three 

 recognized cell elements, came to the conclusion that they were 

 all of common origin, being derived from the primordial germ cells. 

 This conclusion was shortly afterward confirmed by Leuckart ('65) 

 and Landios ('67), but Leydig ('66), on the other hand, questioned 

 this result, and held that only egg and nurse cells are '4n ihrer 

 Wurzel identisch," and ''Epithel hingegen, besteht fiir sich, und es 

 findet kein Uebergang zu dem Keim-und Ei-Zellen statt." Like- 

 wise, Metschnikoff ('66), in his investigation of the embryonic 

 development of Cecidomyia arrived at a similar conclusion namely : 

 that the egg and nurse cells are derived from the "Polzellen der 

 Geschlechtsorgangen," while the epithelial cells have an entirely 

 different history. 



From a study of Nepa and Notonecta, Will ('85), described an 

 entirely new as well as unique method of egg formation, in which 

 both nurse and germ cells arise inside of the large "nuclei'^ 

 filling the terminal chamber of young insects, and w^hich he called 

 " Ooblasten.'" Later, the rupture of the membrane permits the 

 contents of the nuclei to pass out, when the remaining part of 

 the ooblast reconstructs a membrane and becomes a germinal 

 vesicle. Similar processes have been described by Sabattier 

 ('86) and Perez ('86). The latter states that three kinds of nuclei, 

 representing egg, nurse, and epithelial cells, are at first enclosed 

 in a mother cell. 



Will's theory has been severely criticized byKorschelt ('86), who 

 has shown a different origin for these cells in a large number of 

 species. Korschelt supports Claus's idea of a common origin for 

 all three kinds of cells. 



However, Leydig ('89) again produced evidence of a separate 

 origin for germ and epithelial cells, and this view has in latter 

 years been steadily gaining ground. Thus Heymons ('91) showed 

 that in Phijllodromia {Blatta) germanica, the primitive germ cells 

 appear even before the somites are established, while the cells of 

 the terminal thread and the epithelial cells are derived from the 



