108 GERM-CELL CYCLE IN ANIMALS 



We owe the first accurate account of the germ 

 cells in Chironomus to Ritter (1890), who, by means 

 of the section method, showed that the "yolk 

 granules" described by Weismann (1863) in the 

 pole cells are derived from a disc-shaped mass of 

 substance situated near the posterior end of the egg 

 and termed by him the "Keimwulst." Hasper 

 (1911) was able to confirm this discovery, to add 

 other interesting facts, and to correct several of 

 Ritter's errors. The "Keimwulst" of Ritter is 

 called by Hasper the "Keimbahnplasma." 



Ritter advanced the idea that the cleavage 

 nucleus of Chironomus divides within the "Keim- 

 wulst" and that here the first cleavage division 

 occurs, one daughter nucleus remaining in the "Keim- 

 wulst" and becoming the center of the primordial 

 germ cell, the other giving rise to somatic nuclei. 

 This is probably the basis for Weismann's (1904) 

 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. 



According to Hasper one of the cleavage nuclei 



