448 MONTGOMERY. [Vol. XV. 



contains a single large, unstaining globule, which appears as 

 a vacuole (Figs. 162, 175-177) ; or there may be from one 

 to three minute globules in it, which, when seen in their 

 entirety, present the optical appearance (due perhaps to refrac- 

 tion) of black granules, which might be mistaken for solid 

 bodies. The nucleolus has no limiting membrane. The largest 

 are relatively enormous and stain more intensely with eosin 

 than the smaller ones. There is no clear zone in the nucleus 

 around the nucleolus. 



In Linc2is the study of the metamorphoses of the nucleolus 

 is complicated by the occurrence of nuclei in various mitotic 

 stages. Karyokinetic figures were absent in the ovarial stages 

 of the other nemerteans examined, so that in those species 

 the connective-tissue nuclei and the Qgg nuclei both stand in 

 the same cell generation, and the germinal vesicle may either 

 be regarded as equivalent to an ovogonium or to a true ovocyte 

 of the first order. In those species no cell generation separates 

 the connective-tissue nucleus and the germinal vesicle, but the 

 latter is merely evolved from the former by a gradual process of 

 differentiation. But in Linens the germinal vesicle is separated 

 from the connective-tissue nucleus by at least one and prob- 

 ably by two or three generations (if the differences in the size 

 of the cells offer a sure criterion). Here, accordingly, the 

 indifferent connective-tissue cell represents an ovogonium, and 

 perhaps another generation of ovogonia may intervene before 

 the germinal vesicle, the ovocyte of the first order, is produced. 

 Of the two individuals on which these nuclear studies were 

 made, I found mitotic stages in only one individual, while 

 none were to be seen in the other individual, though here 

 these nuclei had reached nearly the same degree of devel- 

 opment. I have studied the mitosis merely with regard to the 

 behavior of the nucleolus. The most abundant stages were 

 those of the spirem and dispirem, asters and dyasters being 

 much less frequent (Figs. 163, 166, 169, 170-172) ; the time 

 duration of the latter stages may be less than that of the 

 former. In by far the greater number of the spirem stages one 

 nucleolus was present ; it is probably present in each nucleus 

 of this stage, but sometimes may escape observation by being 



