5o8 R. W. Hegner 



During the course of the study of the germ-cells in somechryso- 

 melid beetles- a disc-shaped mass of granules (Fig. 9, g, c. d) was 

 discovered in the freshly laid eggs suspended in the peripheral 

 layer of cytoplasm at the posterior end. I have called this struc- 

 ture the "pole-disc." These granules are taken up by the germ- 

 cells in the course of their migration and apparently determine the 

 character of these cells; on this account I have called them "germ- 

 cell determinants" (Hegner '08 h). It was hoped by means of 

 centrifugal force to scatter the granules of the pole-disc and obtain 

 an embryo either without germ-cells or with germ-cells in various 

 parts of the body. It was also thought possible that the pole-disc 

 might move as a w^hole and, becoming massed in some other 

 region of the egg, might influence at this point cells which would 

 ordinarily become body-cells. As will be seen later some data 

 were secured but not enough to warrant any definite conclusions. 



So far as I have been able to learn from the literature no experi- 

 ments with centrifugal force upon the eggs of insects have ever 

 been performed successfully and in only one case has any arthropod 

 egg been tested in a centrifugal machine (Lyon '07). Lyon 

 merely says: "The ovarian eggs of the common garden spider 

 could be separated by one minute's centrifugalizing into two 

 layers" (p. 169). 



The experiments described below were begun at the University 

 of Wisconsin in the spring of 1908 and w^ere continued at the 

 Marine Biological Laboratory at Woods Holl, Mass., where I 

 occupied a room subscribed for by the Wistar Institute of 

 Anatomy and Biology. The material was further studied at the 

 Zoological Laboratory of the University of Michigan. 



II MATERIAL AND METHODS 



During the course of this w^ork eggs of the following beetles were 

 used for experiments: Calligrapha multipunctata, C. bigsbyana, 

 C. lunata, Leptinotarsa decemlineata and Lema trilineata. The 

 posterior ends of these eggs are fastened to the leaf on which they 



2 The Origin and Early History of the Germ-Cells in Some Chrysomehd Beetles. Accepted for 

 publication by the Journal of Morphology. 



