KEIMBAHN-DETERMINANTS 225 



lies, is cut off as a cell which gives rise to the pole- 

 cells. 



In certain Daphnid^, Weismann and Ischikawa 

 (1889) describe a *'Paracopulationszelle" which is 

 derived from the contents of the germinal vesicle 

 (see p. 163) ; but the recent work of Kuhn (1911, 1913) 

 renders it probable that this body is nothing but 

 the remains of a nurse cell. The " Dotterplatte " 

 discovered by Noack (1901) at the posterior end of 

 the egg of Calliphora (Fig. 34) is considered by this 

 investigator to consist of yolk elements. In previous 

 communications (Hegner, 1908, 1909, 1911) the 

 writer has discussed the probability that the pole-disc 

 in chrysomelid eggs consists of nutritive material, 

 and Weiman (1910a) also has offered arguments 

 for this view. 



The granules segregated in certain cleavage cells of 

 Neritina (Blochmann, 1881), Asplanchna (Jennings, 

 1896), Lepas (Bigelow, 1902), Siphonaria (Fujita, 

 1904), and Physa (Wierzejski, 1906) may be of a 

 nutritive nature, and these cells may be the stem 

 cells from which the germ cells of these animals 

 eventually arise. The hypothesis that the nucleoli 

 consist of food substance also argues in favor of the 

 idea that the keimbahn-determinants are nutritive. 



The importance of these nutritive substances 

 to the primordial germ cells can be stated with some 

 degree of certainty. According to some authorities 

 the primordial germ cells remain in the primitive 

 condition and do not undergo differentiation at the 

 same time, or at least at the same rate, as do the 



Q 



