KEIMBAHN -DETERMINANTS 235 



B. THE LOCALIZATION OF THE KEIMBAHN-DETER- 



MINANTS 



One of the characteristics of the keimbahn- 

 determinants is their regular appearance at a certain 

 stage in the germ-cell cycle according to the species in 

 which they occur, and their constant localization 

 in a definite part of the egg, or in one or more definite 

 cleavage cells. Keimbahn-determinants are recog- 

 nizable in many insects' eggs before fertilization is 

 accomplished, and even before the oocyte has reached 

 its maximum size. We know that in Chironomus 

 the "Keimwulst" (Ritter, 1890) or "Keimbahn- 

 plasma" (Hasper, 1911) is present when the egg 

 is laid, at which time the pronuclei as a rule have 

 not yet fused. This is true also of the "Dotter- 

 platte" in Calliphora (Noack, 1901). There can 

 be little doubt, however, that these substances 

 are present as such in the eggs before fertilization, 

 judging from our knowledge of the history of similar 

 materials in the eggs of other insects. The "pole- 

 disc" in the eggs of chrysomelid beetles (Hegner, 

 1908; Wieman, 1910a) and the "polares Plasma" 

 in Miastor (Kahle, 1908; Hegner, 1912, 1914a) are 

 recognizable some time before fertilization and cannot 

 therefore arise because of any influence exerted by 

 the spermatozoon. Moreover, in Miastor the eggs 

 thus far examined have all been parthenogenetic. 

 In parasitic HYMENOPTERA the Keimbahn-chromatin 

 appears in both fertilized and parthenogenetic eggs 

 at an early growth period. In only one animal not 



