STUDIES ON GERM CELLS 383 



nucleus and ''dass nach der Theilung des Furchungskernes die 

 Theilprodukte theils in dem dunklen wulstformigen Korper 

 verbleiben, theils aus demselben herausriicken." 



In 1911 Chironomus was again studied by Hasper, who pub- 

 lished a complete description of the Keimbahn in Chironomus 

 confinis and C. riparius. At the posterior pole of the eggs at 

 the time of deposition is a disc-shaped mass of granules (fig. 1 

 A, kbpl) called by Hasper the 'Keimbahnplasma,' which is 

 identical with the Keimwulst' of Eitter. Hasper characterizes 

 this 'Keimbahnplasma' 



. . . . als dichte, scharf konturierte, wurst- oder flaschenformige, 

 gerundete oder auch in 2 Klumpen getrennte, mit wenigen Vacuolen 

 versehene Masse prasentiert, die am hintern, im Ovarium nach hinten 

 gekehrten Ende des Eies etwas unter der Oberflache leigt, in schaumigem 

 Protoplasma eingebettet, zuweilen aber auch noch ganz von Dotter 

 umgeben. Es ist cliese wichtige Differenzierung des Ooplasmas nichts 

 anderes als jene spezifische Substanz, die bei der Determinierung des 

 ersten von cler Entmcklung dargebotenen embryonalen Materials eine 

 entscheidende Rolle spielt und die daher im Folgenden als Keimbahn- 

 plasma noch mehrfach Erwahnung finden wird (pp. 549-550). 



Ritter ('90) advanced the idea that the cleavage nucleus of 

 Chironomus divides within the 'Keimwulst' and that here the 

 first cleavage division occurs, one daughter nucleus remaining in 

 the 'Keimwulst' and becoming the center of the primordial germ- 

 cell, the other giving rise to somatic nuclei. This is probably 

 the basis for Weismann's ('04) statement regarding his conception 

 of the germ-plasm that 



If we could assume that the ovum, just beginning to develop, divides 

 at its first cleavage into two cells, one of which gives rise to the whole 

 body (soma) and the other only to the germ-cells lying in this body, 



the matter would be theoretically simple As yet, however, 



only one group of animals is known to behave demonstrably in this 

 manner, the Diptera among insects .... 



There is, however, nothing in the literature to warrant the 

 above statement, since Ritter's hypothesis has been disproved 

 by Hasper. 



The primordial germ-cell is really recognizable as such in 

 Chironomus at the four-cell stage (fig. 1, B, p.g.c). One of the 



