No. I.] SPERMATOGENESIS OF BATRACHOSEPS. 49 



spindle and are pulled through the nucleus, later to reappear 

 as retractile fibers, emanating from the apex of the spindle 

 cone. Against the latter assumption speaks the observation 

 that these retractile fibers are not beaded. It seems more 

 probable that the retractile fibers are new formations, and that 

 the contractile fibers have condensed into accessory archo- 

 somes, now appearing on the cytoplasmic membrane around 

 the nucleus. (See explanation of Fig. 112, p. 116.) 



Fiber Cones and Retractile Fibers of the Spindle Cones. 



As spindle cones and their retractile fibers, I designate 

 structures which appear below the nucleus at the end of the 

 anaphase and from which radiate numerous fibers towards the 

 place where the new membrane, separating the two daughter- 

 cells, is being formed. These fibers radiate from a small arch- 

 osome at the apex of the central spindle and end partly in the 

 granules and secretions of the plasmosphere, partly in the cell 

 wall. The separation of the two daughter-cells seems entirely 

 due to these retractile fibers (Figs. 59-61), which are the only 

 ones so situated that they can accomplish such a separation. 

 The plasmospheric granules situated in this immediate vicinity 

 also indicate that they are used up in the construction of this 

 membrane. The ultimate fate of these retractile fibers is a 

 reconstitution into cytoplasm, and perhaps into plasmosphere. 

 They disappear very soon, long before the fibers of the central 

 spindle. 



We have yet to consider the peculiar and unusual structures 

 which I have designated as fiber cones, the origin of whjch is 

 as follows. A new cytoplasmic membrane is formed exterior 

 to the nucleus, and on this membrane are found a number of 

 accessory archosomes. From these archosomes fibers radiate 

 on the membrane in all directions. Later the archosome rises 

 and pulls the membrane with it, and we then get a cone-like 

 structure (Figs, 66-74) which in time pushes out the cell wall. 

 Later on these cones again move inward, and at a yet later 

 stage they dissolve into cytoplasm proper. I have already 

 suggested that these cones help to form a cavity around the 

 nucleus which enables the latter to increase in size and develop. 



