STCDIES ON SEX IN CREPIDULA 25 



observ'ed running through the middle of the axial plate (fig. 

 40a). A cross section through the cell body of a stage similar 

 to figure 38 (fig. 406) shows the core surrounded by axial fibers. 



Nothing has so far been said concerning the number of the 

 centrioles. It has not been found possible to count them in the 

 early stages, because of the presence of other structures with 

 which they may be confused. For instance the cytoplasmic 

 granule seen in the early spermatoblast stage sometimes appears 

 to persist after the disintegration of the nucleus; and there are 

 often minute particles of chromatin free in the cytoplasm which 

 are difficult to distinguish from the centrioles. In the adult 

 apyrene spermatozoon, however, the fibers lie at the peripherv- 

 of the cytoplasm, somewhat separated from one another, so that 

 they can be observed in cross section. There appears to be 

 either eight, nine or ten of them; it is possible that there is a 

 constant number, some staining indistinctly and being over- 

 looked; in which case the largest number counted flOj would be 

 the correct one. The number of fibers would be (supposedly) 

 the same as the total munber of centrioles before the formation 

 of the axial bundle. Actually the number of fibers in the adult 

 apjTene spermatozoon seemiS to be less than the number of cen- 

 trioles which congregate at the edge of the sperooatosome, but 

 this again is uncertain on account of the possible confusion of 

 centrioles with chromatic elements, etc. The possibility is sug- 

 gested that some of the fibers have taken a central position and 

 become the core of the spermatozoon. 



Returning now to the nuclear vesicles : in the young spermato- 

 some these were composed of a shell of chromatic material sur- 

 rounding a coarse chromatic reticulum. While the axial bundle 

 is increasing in length the reticulum becomes gradually lost, 

 lea\Tng only a chromatic capsule containing a clear nuclear sap 

 or kar\'olymph (figs. 34, 35, 36). From this point on there is a 

 gradual dissolution of the nuclear vesicles, the thinner parts of 

 the capsule disappearing first and lea\'ing the thicker portions as 

 crescentric bodies which themselves finally vanish. The chro- 

 matin has always disappeared before the cytoplasm of the cell 

 is all disposed upon the axial bundle. 



