STUDIES ON GERM CELLS 463 



In the particular cases to be discussed here the nucleoh are not 

 temporary structures, as is usually true, but persist for a com- 

 paratively long interval after the germinal vesicle breaks down. 

 The most important and convincing evidence of the functioning 

 of a nucleolus as a Keimbahn-determinant is that furnished by 

 Silvestri ('06, '08) in parasitic Hymenoptera. Here, as shown 

 in figures 13 and 14 and described on page 429, the nucleolus es- 

 capes from the germinal vesicle, comes to lie a considerable dis- 

 tance away at the opposite (posterior) pole of the egg, and later 

 is segregated in the cytoplasm of the germ cells, apparently play- 

 ing some role in the determination of the latter. Several events 

 in the history of this nucleolus are unusual. (1) The nucleolus 

 leaves the germinal vesicle before the nuclear membrane dis- 

 solves, whereas usually this body is not cast out into the cytoplasm 

 until after the spindle has begun to form; (2) The nucleolus 

 does not become granular and disappear but persists intact for 

 a considerable period; (3) It comes to occupy a definite position 

 in the egg, i.e., at the posterior pole; (4) During cleavage the 

 nucleolar material becomes distributed apparently equally among 

 all of the primordial germ cells, and is absent from all of the 

 somatic cells. Silvestri has given us no data regarding the 

 escape of the nucleolus from the germinal vesicle and the writer 

 is at present unable to account for this peculiar behavior, al- 

 though he is now at work on the growing eggs of a polyembryonic, 

 hymenopterous parasite which he hopes will enable him to de- 

 termine this point, as well as to trace the history of the nucleolus 

 back into early stages.'^ 



As we have already noted, in a few instances the nucleolus 

 does not disappear during the maturation divisions but persists 

 for a time as a 'metanucleolus' (p. 457). The nucleoli of these 

 parasitic Hymenoptera are of this sort. They are evidently of 

 a different nature from the usual type and arelience saved from 

 immediate disintegration in the cytoplassm. The localization 

 of this nucleolus at the posterior end of the egg is the result, 



2 This has since been completed and published in the Anat. Anz., Bd. 46, 

 pp. 51-69, 1914. 



