282 The Ohio Naturalist. [Vol. VIII, No. 5, 



could not be accurately represented by anything less than the 

 heavv lines in the drawing. Since the rays are cylindrical rods 

 rather than plates the membrane is not a first any membrane 

 at all but a cage around the vacuole. The method by which the 

 interstices between the bars are filled up could not be followed 

 satisfactorily. But it may be that the substance of the rays 

 gradually spreads out around the vacuole till the membrane is 

 completely formed. This process may be seen on the side of the 

 nucleus towards the centrosome in those cases where the apex of 

 the cone of rays is very acute. Here the rounded surface of the 

 vacuole may be seen to acquire a membrane like that of the rest 

 of the nucleus so gradually that i'c is often difficult to tell whether 

 the membrane is present or absent (fig. 11). In these cases the 

 cap of rays persists for a considerable time but gradually fades 

 when the membrane is complete (figs. 10,11). 



This method of the formation of the nuclear membrane by 

 the rays of the centrosome has been observed by the writer in 

 very many cases; to the five figures given to illustrate the stages 

 of the process could be added many more if it vrere deemed 

 necessary . 



Aside from the peculiar method of its formation, the nuclear 

 membrane of Synch\trium is a remarkable structure. In the 

 primary nucleus it reaches a relatively enormous thickness (See 

 Stevens '03, fig. 5) and it is so stifi: that it is often broken and 

 carried awav by the knife. In the succeeding mitoses it is not 

 only thickened but sometimes presents some very peculiar aspects 

 which we shall hope to deal wirh in a later paper. One feature 

 may be touched upon here. 



Those rays which form the m.embrane, like the others, fre- 

 quently have granules strung a'ong them. In other rays the 

 granules are centrally placed on the ray but in these they are 

 nearly always found on the inside of the nuclear cavity (figs. 4, 

 7, 8)'. In older stages they may be found either within the 

 nucleus, in the v^-all, or lying against its outer edge (fig. 12). Per- 

 haps, correlated with these granules are others f.-equently seen 

 loose in the cytoplasm, and surrounded each by a vacuole of its 

 own (fig. 11). Rut consideration of these would carry us too 

 far afield. We can not do more at this time than to suggest the 

 possible analogy betv.een the formation of these granules and 

 the derivation of the microsomes of the c\toplasm from the 

 nucleus as described by Lillie and others. 



Summary. The exact history of the structures touched inci- 

 dentally, the aste.'S and ihe chromatin content of the nucleus, is 

 somewhat pf-ovisional, \)\\\ the poinc of the present paper is the 

 demonstration, confirming and amplifying Kusano's announce- 

 ment that the rays of the centrosome enclose the vacuole surround- 

 ing the naked clrromosomes, ami fo.-ni a very heavy deeply 

 staining membrane around it. the nuc'ea; meml).-anc. 



