No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 425 



The cycle of the formation of the nucleoli may here also be 

 divided into three stages, which do not quite correspond to the 

 four of Aviphiponis gelatinostis . 



First nucleolar stage. — In the smallest germinal vesicles 

 found one or two relatively very large nucleoli were present, 

 one of them often in the center of the nucleus, the other 

 more excentric or even against the nuclear membrane (Figs. 

 103, 114, 115). The nucleoli in these smallest nuclei are 

 as large or nearly as large as in any of the following stages. 

 In germinal vesicles of slightly greater dimensions three or four 

 nucleoli may be present, and some of these may have increased 

 a little in size ; the amount of nucleolar substance at this stage 

 is often so great as to occupy a fifth of the nucleus. They 

 now increase in number, until at the close of this period we 

 find a considerable number of mostly large nucleoli quite evenly 

 distributed through the nucleus (Figs. 104-106, 109, no, 116), 

 but often they are at one of its poles more numerous than at 

 other points. This stage would seem to correspond to the first 

 and second of Amphiporus glutinosus. 



Second nucleolar stage. — The nucleoli continue to increase 

 in number but now decrease in size and commence to pass to 

 the periphery of the nucleus, until at the end of this period 

 they all lie close to the nuclear membrane, are regular in out- 

 line, and adequal in size (Figs. 107, 119, 122, 124-126, 130, 131). 

 At the beginning of this stage numbers of nucleoli may be 

 found arranged in chain-like rows, as is to be seen in Fig. iii. 

 This would correspond to the third stage of Amphiporus. 



Third nucleolar stage. — Nearly all the nucleoli are close to 

 the nuclear membrane, often flattened against it (Figs. 1 17, 120, 

 127, 129, 137, 138). They show signs of degeneration; thus 

 they stain less intensely, are irregular in outline, and have a 

 vacuolar or granular structure. In the largest germinal vesicles 

 their number has apparently decreased and small non-coherent 

 masses of granules may be seen, which are probably degen- 

 erated nucleoli. Sometimes a nucleus may be found in this 

 stage in which almost all of the nucleoli contain each one 

 large, excentric, lightly stained globule or vacuole (Fig. 1 17). 

 Staining of the nucleoli. — The natural color would appear 



