THE GERM-CELLS OF CICADA (xiBICEN) SEPTEMDECIM. 417 



middle points. As the strepsistene stage advances, the threads 

 lengthen considerably, become more lightly staining, and as 

 they separate more widely their individuality becomes less and 

 less distinct. In the older oocytes, the chromatin of the germinal 

 vesicles appears more or less granular, much of it still retaining 

 its affinity for the basic stains. On close analysis of such nuclei 

 (Figs. 46, 47) much of the chromatin shows evidences of still 

 retaining, in part, the arrangement in threads, and I interpret 

 these as being the original conjugating threads of the early 

 growth stages which have been greatly expanded. 



4. Chromatin Nucleoli. 



I shall not attempt to review the literature concerning nucleoli 

 since there is considerable confusion of interpretation in this 

 field. It is evident that many of the different opinions expressed 

 in the literature have arisen from the fact that these structures 

 are not always homologous. Recently Nakahara ('18) has 

 advanced the view that in the oocytes of Perla, the nucleoli are 

 derived from the yolk-nucleus which consists of a dense granular 

 mass in the cytoplasm closely applied to the nucleus. As will 

 be shown later, Nakahara's "yolk-nucleus" is really an accumula- 

 tion of mitochondria, and it is difficult to see how these could 

 give rise to nucleoli. 



In the oocytes of Cicada true chromatin nucleoli are found, and 

 whenever they are present take the basic stains. The interest 

 connected with chromatin nucleoli in the oocyte is bound up 

 with the possible homology of such structures with the chromo- 

 some nucleoli or persisting sex-chromosomes found in the growth 

 stages of the spermatocyte. Since one sex-chromosome of the 

 female is derived from the sperm, there is no a priori reason why 

 we should not expect to find such a body persisting in the stages 

 in the oocyte homologous to those stages in the spermatocyte 

 where it is found to persist as a nucleolus. 



In the very young oocyte of Cicada (Figs. 35, 36, 73, 74), there 

 are usually present two chromatin nucleoli. In the leptotene 

 nuclei these are no longer found, nor can they be found in the 

 succeeding pachytene stages. However, in the strepsistene 

 nuclei, two deeply staining bodies again appear (Figs. 43, 78) 



