No. 2.] COMPARATIVE CYTOLOGICAL STUDIES. 5 19 



relation to those of the first generation ; and their difference 

 from the latter is probably due to the fact that they have been 

 produced at a time when very different physiological conditions 

 exist in the nucleus. 



It is not my intention in this contribution to deal in any 

 detail with those cases where double nucleoli occur in a cell, or 

 those where two chemically and morphologically different kinds 

 of " nucleoli" occur in the same nucleus ; to these cases it is 

 my intention to devote a special study. But preliminarily, from 

 those observations which I have made on this subject, the 

 following conclusions are in order. In a nucleus there some- 

 times occurs a double nucleolus, the component parts of which 

 may each represent a true nucleolus ; or such a double nucle- 

 olus may consist of a true nucleolus apposed to a chromatin- 

 nucleolus (according to my unpublished observations on the 

 spermatocytes of the beetle Harpalus). Further, and this is fre- 

 quently the case in resting spermatocytes of the first order, the 

 nucleus may contain a true nucleolus separated from a chromatin- 

 nucleolus ; and in Peniatoma, the account of the spermatogenesis 

 of which will be shortly published by me, the unique process 

 occurs of the chromatin-nucleolus being a metamorphosed 

 chromosome (one of the fourteen chromosomes of the last 

 spermatogonic division becoming the chromatin-nucleolus of 

 the first spermatocyte) ! This peculiar structure of Pentatoma 

 divides with the true chromosomes in the first reduction divi- 

 sion. In another case where I have been able to follow all 

 the developmental stages of a chromatin-nucleolus, namely, in 

 cells of the hypodermis of the larva of Carpocapsa, I found it 

 to originate from one of the granules of the nuclear reticulum, 

 — a particular one of these granules (karyosomes) gradually 

 increasing in size until it attains large dimensions ; during its 

 growth period it is usually attached to one of the true nucleoli 

 of the cell. What is of importance in these two cases {Poita- 

 toma and Ca)pocapsa) is the distinction emphasized between the 

 true nucleolus and a karyosome or chromatin-nucleolus : the 

 latter always standing in genetic connection with the true 

 chromatin, while the former, so far as my observations go, is 

 never derived from this substance. These observations are not 



