192 



MONTGOMERY — A STUDY OK THE CHROMOSOMES 



35. Sinea diadema Fabr. 



Two testes of this species were studied. 



The relations of the chromatin nucleoli in the rest stage of the spermatogonia could 

 not be determined. 



There were on my preparations only a few sperm atogonic monaster stages, and none 

 of these were favorable for determining the number of chromosomes ; the chromosomes 

 are small, densely grouped, and particularly minute elements among them might be 

 chromatin nucleoli. 



In the rest stage of the spermatocyte arc present four small chromatin nucleoli (iV. 

 2, Figs. 212, 213, PI. V), all of them attached to the surface of a large true nucleolus (JV). 

 One is larger than the others, and appearing on lateral view to be always transversely con- 

 stricted (Fig. 213) is probably bivalent; and as one of the three smaller ones is some- 

 limes found to be bipartite, this too would be bivalent. The two remaining are appar- 

 ently always spherical and not transversely constricted, so that they would seem to be 

 univalent. If this interpretation is correct, there would be here two bivalent chromatin 

 nucleoli each with its component parts closely apposed, and one bivalent one with its 

 components separated, that is three bivalent ones in all ; and in the first maturation divi- 

 sion there are three chromatin nucleoli present (Figs. 214, 215), which would corroborate 

 this conclusion. But since it could not be determined how many there arc in the sperma- 

 togonia, the relations in the spermatocytes cannot be considered positively demonstrated. 



Pole views of the monaster stage of the first maturation division (Figs. 214, 215) 

 show always three minute chromatin elements, which are chromatin nucleoli (N. ,'i 1 ), and 

 apparently thirteen larger chromosomes. But a careful examination of these Larger 

 elements shows that in every Case four bivalent chromosomes form together a plurivalenl 

 one, all lour being closely apposed and with (heir long axes parallel to one another. 

 This is best seen on lateral view of the spindle (Figs. 217, 218), where the four chromo- 

 somes marked t are always found to he grouped elose together; in Fig. 216 only these 

 four chromosomes with their mantle fibre attachments are seen on lateral view. Of the 

 four chromosomes thus grouped together, the two middle ones stand in the closest apposi- 

 tion (Fig. 216-218) ; and on pole views these two middle ones may be so closely apposed 

 as to appear as oik; Long one (/, Fig. 214), or a slight transverse constriction marks the 

 division line between them (/, Fig. 215). It follows accordingly that the three elements 

 seen on pole view and marked / are really four bivalent chromosomes, the two central ones 

 being so closely apposed as to appear generally as one long one. A comparison of the 

 elements designated / in Figs. 214 and 215 with the corresponding elements in Figs. 21<>- 

 218 makes this evident. Accordingly there are really fourteen bivalent (dumbbell-shaped) 



