GAMETOGENESIS OF SACCOCIRRUS 21 



have a stout triangular base quite like the bodies in PI. 3, 

 fig. 23. 



When I came to examine my first preparations illustrating 

 the oogenesis of Saccocirrus, I did not immediately notice 

 the fine mitochondria drawn in PI. 3, figs. 22 and 23, and I was 

 temporarily led to believe that the nucleolar extrusions might 

 represent the mitochondria. But before 1 had made more and 

 better preparations, as the result of my experience on this new 

 material, my belief in this view that the nucleoli might represent 

 mitochondria was shaken by finding such cells as that in PI. 1, 

 fig. 3, in which I noted both mitochondria and bodies which, 

 I concluded, represented the extruded nucleoli of the oocyte. 



With regard to the probable reason for the appearance of 

 nucleolar extrusions in a spermatocyte, I believe that it is 

 due to the fact that such cells are packed away among yolk- 

 cells which bring about conditions simulating the metabolism 

 of the egg-cell. 



10. Discussion. 



(a) General. 



The oogenesis of Saccocirrus is likely to be typical of several 

 other Annelida, and possibly of Polychaeta such as Chaeto- 

 pterus and Nereis, judging from Lillie's figures of centrifuged 

 ova of these genera. 



A graphic representation of the oogenesis of Saccocirrus 

 would be as follows : 



Oogonium. Full-grown Oocyte. 



1. Nucleolus. 



2. Nucleolar deutoplasm or nucleolar 



yolk-spheres. 



-,_,,., , (3. Definitive Golgi elements. 



2. Golgi elements • l . ^r ,, i /^ 1.1. \ 



° (4. Yolk-spheres (fatty). 



3. Mitochondria . 5. Mitochondria. 



4. Chromosomes . 6. Chromosomes only. 



The part of this scheme about which I feel some doubt is 

 the metamorphosis of the Golgi element into a yolk-sphere ; 



1. Nucleolus 



