Further Studies on Reproduction in Sagitta. 289 



wall seems to be the opportunity to open a way to the exterior. 

 Failure to make their way into the oviduct may be the whole 

 explanation of the conditions observed. The eggs are already 

 fertilized and therefore ready to go on developing unless some 

 added stimulus from the sea-water were necessary to cause them 

 to complete their maturation and begin to segment. That this 

 is not the case is evident; after the egg is fertilized and has broken 

 away, maturation and the early segmentation stages go on whether 

 the egg is laid at the normal time or is retained in the ovary. 

 Most of these eggs had decidedly irregular outlines suggesting 

 amoeboid movements and supporting my conclusion that the 

 eggs make their way into and down the oviduct by their own 

 activity. 



Elpatiewsky's 'Besondere Korper' 



The appearance of Elpatiewsky's ('09) paper on "Die Urge- 

 schlechtszellenbildung bei Sagitta" invests these segmenting eggs 

 with a new value. Elpatiewsky finds in the development of 

 normally laid eggs a stainable body which, from the first segmenta- 

 tion on, marks the germ track ; and, possibly, is in the sixth division 

 the determining factor in the separation of the germ plasm into pri- 

 mary oogonia and primary spermatocytes. This 'besondere 

 Korper,' as Elpatiewsky designates it, is first seen near the vegetal 

 pole of the egg when the two pronuclei are in the center of the egg, 

 and the first cleavage plane passes a little to one side of it. Al- 

 though Elpatiewsky states that he first finds this homogeneous 

 stainable body in the stage where the two pronuclei are uniting, 

 my first thought on reading the paper was that this body must 

 have some relation to the accessory fertilization cell which I had 

 described ('05) as degenerating after the egg breaks away from 

 the oviduct wall. This description was based on the degenerate 

 appearance of the cell in eggs nearly ready to break away, and on 

 the fact that I had been able to find no trace of it in the eggs 

 after they entered the oviduct. Indeed, I suspected that in some 

 cases the accessory cell might be actually pulled out of the egg. 



