408 ROBERT W. HEGNER 



removed constituted a source of error which made the results 

 uncertain. 



A second set of experiments (Hegner '11a) were therefore de- 

 vised and a method employed which made it absolutely certain 

 that the pole-disc could not take part in the development. In 

 these experiments the posterior end of the egg was touched with 

 a hot needle and that portion containing the pole-disc was 

 killed. In every instance the development continued and the 

 blastoderm formed normally over all of the surface except at 

 the posterior end ; here it was built at the end of the living sub- 

 stance as shown in figure 8, C, bl. No germ cells were produced, 

 as in the normally developed egg at this stage (fig. S, D). I 

 conclude from this that the pole-disc granules or the substances 

 in which they are imbedded are necessary for the formation of 

 germ cells. 



B. Nuclear division and differentiation in the eggs of Chrysomelid 



beetles 



This work was undertaken in order (1) to determine whether 

 or not a chromatin diminution process takes place in the cleavage 

 nuclei of Chrysomelid eggs similar to that described in Ascaris 

 by Boveri ('92) and in Miastor by Kahle ('08) ; (2) to study the 

 differentiation of the nuclei which take part in the formation of 

 the primordial germ cells, blastoderm cells, and vitellophags; 

 and (3) to record what appears to be amitotic nuclear division 

 among the vitellophags. 



General account of early cleavage. Eggs of Calligrapha multi- 

 punctata, C. bigsbyana, and Leptinotarsa decemlineata have 

 been used for this purpose. Beetles were kept in the labora- 

 tory in Stender dishes and closely watched, so that the exact 

 interval between the time of deposition and time of fixation 

 could be determined. Eggs were killed in Tower's second solu- 

 tion heated to the boiling point. The chorion was dissected off 

 aftgr a few days and no difficulty was encountered in imbedding 

 in paraffin and sectioning. Because of the abundance of yolk, 

 Mayer's acid hemalum was used principally for staining pur- 



