^16 ^MONTGOMERY. [Vol. XV. 



frequent in many egg cells, infrequent in somatic cells of the 

 Metazoa, and apparently never present in plant cells. In each 

 such egg cell there may be either one nucleolus proper and 

 from one to several paranucleoli (this being the most usual case), 

 or there may be a single paranucleolus and a few nucleoli 

 proper. In the ova of three forms examined by me there were 

 two kinds of nucleoli present, namely, in Montagua, Polydora, 

 and Rodalia. In my descriptions I have employed the term 

 " pseudonucleolus " for these secondary nucleoli, since in this 

 form they have a different structure from that of the nucleolus 

 proper, but nevertheless stain in the same way, so it is difficult 

 in this case to decide whether they correspond to paranucleoli, 

 and hence I have used the indifferent name "pseudonucleoli" 

 for them. In Polydora we found from one to three paranucleoli 

 in the larger germinal vesicles, and these are always apposed to 

 the nucleolus. Then the smaller, deeply staining bodies in the 

 maturer stages of the ovum of Rodalia may be comparable to 

 paranucleoli. Whether the remarkable structures of the germi- 

 nal vesicles of Tetrastemma catejiiilatiim are paranucleoli, I am 

 wholly unable to decide. This problem of different types of 

 true nucleoli in the same nucleus is one of the most difficult 

 in the study of nucleolar structures, so that it is necessary to 

 discuss it more in detail. 



A. Schneider ("83), Brauer ('9i), and Floderus ('96) consider 

 the paranucleoli to be derivatives of the nucleolus proper, more 

 especially to be buds from its surface. Hacker ('93a) considers 

 them to be secretions of the chromatin. Flemming ('82) doubts 

 whether " die Unterscheidung von Haupt- und Nebennucleolen 

 eine durchgehende Geltung beanspruchen kann "; he finds that 

 in Anodonta the two are at first in contact, but that later they 

 become separated. Giard ('8l) finds in the ovum of a Spionid 

 one nucleolus, and later there appears in the nucleus a much 

 smaller body, which fuses with the former. Lonnberg ('92) 

 thinks that the paranucleoli may serve for the acquisition of 

 nourishment, or may contain reserve nourishment. List ('96) 

 considers that the paranucleoli and the nucleoli of the somatic 

 cells are more closely allied to one another than to the nucle- 

 olus proper of the ova, and that the former two " mindestens 



