1^8 BIOLOGICAL LECTURES. 



which accordingly may differ chemically, nucleoli are produced 

 which are not chemically homogeneous throughout ; this seems 

 to be the case in the ova of numerous arthropods {e.g., Gryllus, 

 Eiichistiis, Phalajigopsis, and other insects). 



Amoeboid movements have been observed in life by numerous 

 authors. But from the probable nature of the nucleolus, which 

 will be discussed below, the conclusion seems probable that all 

 movements, fusions, and divisions are passive in regard to the 

 nucleolus ; that they are not spontaneous movements of the 

 nucleolus, but due rather to chemical dissolutions and changes. 

 This is in agreement with Rhumbler's conclusions. 



Besides the movements due to change of form, in which 

 process divisions and fusions are frequently concerned, there 

 remain to be considered those of change of location. The 

 migration of nucleoli in the germinal vesicles of Nemerteans 

 has been already considered ; and such migrations are possibly 

 of general occurrence in all cases where the number of nucleoli 

 is large. Besides such phenomena, migrations of nucleoli into 

 the cytoplasm in the resting cell have been frequently described. 

 Among others may be mentioned the conclusions of Roule 

 in Ascidian ova, to the effect that such nucleoli eventually 

 become nuclei of new cells, and similar observations on endo- 

 genetic cell formation in molluscan ganglion cells, as described 

 in a recent paper by Rohde. But it is hardly necessary to 

 remark that all recent cytological studies render it very prob- 

 able that no such endogenetic cell formation occurs in the 

 Metazoa. Among the numerous objects studied by me, only 

 one was found showing in the resting cell a migration of 

 nucleoli into the cytoplasm, but that one, now to be described, 

 proved to be of a unique character. 



The clitellar gland cells of Piscicola are cells of enormous 

 size, to be readily seen with the naked eye, which occur in the 

 body cavity throughout the whole length of the worm, except in 

 the cephalic region, and the ducts of which open in the region of 

 the genital pores. During the process of formation of their 

 secretion two main stages may be distinguished : a prophascy 

 from the stage of the young cell until all the secretion has 

 been formed and the cell has attained its maximum dimensions ; 



