384 ROBERT W. HEGNER 



♦ 



first four cleavage nuclei migrates to the posterior end, and, 

 separating from the rest of the egg together with the 'Keim- 

 bahnplasma' and the cytoplasm in which this substance lies, 

 forms the 'Urgeschlechtszelle.' The primordial germ cell is 

 undergoing division by mitosis at the time when it is protruded 

 from the egg and during this process the 'Keimbahnplasma' 

 is apparently equally divided between the daughter cells. 



Wahrend die ersten Teilungen rasch aufeinander folgen, kommt die 

 letzte gar nicht mehr sur Vollendung, d.h. sie erstreckt sich nur auf 

 die Kerne, so dass schliesslich 8 zweikernige Genitalzellen im hintern 

 Polraum liegen. Und damit ist die Entwicklung der Keimbahn fiir 

 lange Zeit liberhaupt abgeschlossen; denn wahrend der nun folgenden 

 Embryonalperiode ist sie durch ein durchaus passives Verhalten ausge- 

 zeiehnet (p. 553). 



One of these binucleated germ-cells is shown in figure 1, C. 



It is unnecessary to trace the history of these primordial 

 germ-cells (pole-cells) since it has been shown repeatedly that 

 they give rise to the oogonia or spermatogonia in the definitive 

 germ-glands. Portions of the 'Keimbahnplasm' persist at least 

 until the larva hatches (fig. 1, D). The origin and nature of the 

 'Keimbahnplasm' was not discovered by Hasper but the name 

 applied to it and the fact that the author adopts my term 'germ- 

 cell determinants' (Keimzelldeterminanten) in discussing it, 

 indicate that he considers it of fundamental importance in the 

 segregation of the germ-cells. 



The possibility of determining the origin of the 'Keimbahn- 

 plasma' of Chironomus led the writer to study the oogonia in 

 the terminal chamber and the various stages in their growth up 

 to the time of deposition. Larvae were collected and allowed to 

 develop in the laboratory and the ovaries were dissected out of 

 the adults which were obtained from these larvae. However, 

 the material procured has been found lacking in both the 

 earlier stages of the development of the oocytes and the late 

 stages in ' the formation of the ovum. It has been considered 

 best, therefore, to reserve a study of this material until a com- 

 plete series can be secured. 



