STUDIES ON GERM CELLS 401 



large size, larger nuclei, and more deeply staining cytoplasm. 

 The germ-cells did not stop when they reached the surface of 

 the egg, but passed outside and became separated from it; their 

 number increased .... peu a peu par suite de Farrivee 

 de nouvelles cellules peripheriques et aussi sans doute de la divi- 

 sion des premieres cellules detachees du pole de I'oeuf." The 

 germ-cells then started to re-enter the egg, retarding, by this 

 migration, the formation of the blastoderm at this point. 'Tin- 

 alement, le blastoderme acheve de se former au pole posterieur 

 de Toeuf, et alors les cellules sexuelles se trouvent groupees. 

 . . . . entre le vitellus et I'enveloppe blastoderniique." 



Several species of Chrysomelid beetles were also studied by 

 Friederichs ('06), who discovered that the cleavage nuclei in 

 Donacia crassipes reach the posterior later than the anterior end 

 of the egg; the reverse is the rule in species of allied genera. 

 After the blastoderm is formed "an der Ventralseite unmittelbar 

 seitlich vor dem Pol, findet eine besonders lebhafte Zellvermeh- 

 rung statt, so dass einzelne Zellen aus dem Blastodermverband 

 heraus und ins Innere gedrangt werden." These, the primitive 

 germ-cells, were not very different in Donacia from blastoderm- 

 cells, but in Timarcha nicoeensis and Chrysomela marginata 

 they could be distinguished by the larger size and darker color 

 of their nuclei. 



In a series of papers published within the last six years, the 

 writer has given the results of morphological and experimental 

 studies on the primordial germ cells of Chrysomelid beetles, par- 

 ticularly Calligrapha bigsbyana, C. multipunctata, C. lunata, 

 and Leptinotarsa decemlineata. It has been possible to trace 

 the entire Keimbahn in these insects, and to carry on experi- 

 ments with the eggs and embryos without preventing further 

 development. The reader is referred to the original papers for 

 details, but a general account will be given here as an intro- 

 duction to the. original work to be presented in the succeeding 

 pages. 



At the time of deposition, the eggs of the Chrysomelid beetles 

 studied are not always in the same stage of development, al- 

 though usually polar body formation is taking place. The egg 



