274: Robert Wilhelm Hegner. 



Blochniann. It is liighly probable that a 5imib\r expulsion of nuclear 

 material and corresponding decrease in the size of the germinal 

 vesicle takes place in the oocytes of Chrjsomelid beetles, and that the 

 particles of chromatin thus set free gather at the posterior end of 

 the egg to form the pole-disc/ 



Wheeler's (1897) theory to account for the presence of dark- 

 staining granular inclusions within the eggs of Myzostoma glabrum 

 suggests that the granules of the pole-disc may be derived from the 

 nuclei of the nurse-cells which, in many insects, pass into the early 

 oocytes. 



The results that Hacker (1897) obtained from a study of the 

 "Keimbahn" in Cyclops also point to a nuclear origin of the pole- 

 disc granules. According to this author "Ausseukornchen" arise at 

 one pole of the first cleavage spindle ; these are derived from dis- 

 integrated nucleolar material and are attracted thus to one pole of 

 the spindle by a dissimilar influence of the centrosomes. During 

 the first four cleavage divisions the granules are segregated always in 

 one cell ; at the end of the fourth division these "Ausscnkornchen" 

 disappear, but the cell which contained them can be traced by its 

 delayed mitotic phase into the primitive germ-cells. The "Aussen- 

 kornchen" found in the germ-cell antecedents of Oy clops show a 

 remarkable resemblance to the pole-disc granules of Calligrapha; 

 one important difference, however, may be pointed out, i. p., the fact 

 that in the formPT the granules arise from the nu'^leolar material 



'Since this paper was sent to press an account of the origin of the pri- 

 mordial germ-cells in some parasitic Hymenoptera has appeared which fur- 

 nishes proof of the nuclear origin of a structure similar to the pole-disc. I 

 refer to the work of F. Silvestri, entitled Gontribiizioni alia cnnosccnza hio- 

 logica degli imenotteri parassiti, published in the Bollettino del LaJwratorio 

 di soologia gcnerale e agraria della R. Scuola Superiore d' Agricoltura di 

 Portici, Vol. 3, April, 190S. The following qinotation gives some of the 

 results of his study of Ageitkispis fuscicoUis. "Che il nucleolo durante la 

 formazione dei globuli polari si conserva inunutato nella parte posteriore 

 deir ovo e che passa interoi ad una delle prime due cellule di segmentazione. 

 Tale nucleolo, come nel Litomastix trwicatelliis, ha un' azione ritarda trice 

 della divisione della cellula, in cui si trova ed e da ritenersi, per quanto 

 ho anche osservato nello sviluppo delle due specie, di cui appresso tratto, un 

 dot'erminante della celulle germinali" (p. 53). 



