448 ROBEET W. HEGNER 



gradually disappear, apparently dissolving, and, in' the four 

 germ cells resulting from the next division, only occasionally 

 can stained granules from this body be distinguished. 



Buchner ('10a, '10b) had no difficulty in finding the 'besondere 

 Korper' of Elpatiewsky and in tracing it during the cleavage 

 stages. He claims that it originates from the 'accessory fertili- 

 zation cell' described by Stevens ('04) as degenerating after 

 the egg breaks away from the oviducal wall, and that it is chro- 

 midial in nature and should therefore be called 'Keimbahnchro- 

 midien.' Stevens ('10), however, has carefully examined abun- 

 dant material from Sagitta elegans and S. bipunctata and could 

 trace no connection between the 'accessory fertilization cell' 

 and the 'besondere Korper,' the latter appearing for the first 

 time at the stage when the egg and sperm nuclei lie side by side 

 in the middle of the egg, thus confirming Elpatiewsky's con- 

 clusions. She admits the possibility of the origin of the 'beson- 

 dere Korper' from granules of the accessory fertilization cell, 

 provided this material loses its staining capacity for a period, 

 and suggests also that the granules of chromatin-like material 

 extruded from the nucleus of the egg during maturation may 

 take part in its formation. Miss Stevens also believes with 

 Elpatiewsky that the 'besondere Korper' divides unequally 

 between the two daughter cells of the primordial germ cell and 

 that this is a differential division. She was unable, however, 

 to detect any constant difference between either the cytoplasm 

 or the nuclei of oogonia and spermatogonia. It is worthy of 

 mention that Elpatiewsky ('10) believes that the 'besondere 

 Korper' may originate ''aus dem achromatischen Kernkorper." 



The differentiation of oogonia and spermatogonia from indiffer- 

 ent germ cells during the development of hermaphrodites is a 

 subject of great interest and importance. Attempts have been 

 made, especially with molluscs (Ancel '02, '03; Buresch, '11; 

 Boveri, '11; Schleip, '11), but without as definite results as are 

 desirable. The early differentiation of germ cells into oogonia 

 and spermatogonia in Sagitta, which was pointed out by Hert- 

 wig ('80), has been employed by Pedaschenko ('99) as a basis for 

 a theory of sex determination in a copepod, Lernaea branchialis. 



