122 Transactions of the Society. 



J. H. "Woodger, of University College, for kindly fixing some of 

 the material used in this research, during my absence. 



Previous Work on the Nucleolus. 



It is customary to recognize three types of nucleoli within the 

 nuclei of various cells — namely, plasmosomes, karyosomes and 

 amphinucleoli (i). The plasmosomes, or " true nucleoli " are 

 usually spherical bodies, composed of " plastin " whose staining 

 reaction is oxyphil — that is, they take up acid stains such as eosin. 

 The term karyosome is usually applied to nuclear granules whose 

 histo-chemical reactions are similar to those of chromatin ; such 

 bodies stain with dyes like hsematoxylin and methyl green, and 

 are therefore spoken of as basophil. Amphinucleoli are believed 

 to be composed of a mixture of " chromatin " and " plastin " ; 

 they occur in many Protozoa. Their staining reactions are inter- 

 mediate between those of plasmosomes and karyosomes. 



Our knowledge of the relationship of the nucleolus to the 

 metabolism of the cell is very fragmentary. Nucleoli at different 

 times have been regarded as storehouses of either albuminous 

 compounds, or chromatin, or both combined, as accumulations of 

 waste products within the nucleus, or as special nutritive organs 

 concerned either with the metabolism of the cell, or else with the 

 elaboration of chromatin from the karyolymph. 



Piecently, emphasis has been laid upon the importance of the 

 nucleolus by Carleton (^), who has shown that within the nucleolus 

 of epithelial cells of the gut of the cat and frog there is an argento- 

 phil core consisting of several granules. During cell division, 

 while the greater part of the nucleolus disintegrates, these granules 

 persist and pass in about equal numbers to each of the newly 

 forming cells, where a new nucleolus is formed around them. 

 Such intranucleolar bodies have been found associated with both 

 plasmosomes and karyosomes. 



Actual fission of the nucleolus can be observed during amitosis 

 of follicle cells in the ovaries of insects. In those of Dytiscus, 

 which have been prepared by fixation in Bouin's fluid and stained 

 with Mann's methyl blue eosin, I find a distinct oxyphil nucleolus. 

 This elongates, becomes dumb-bell shaped and eventually separates 

 into two distinct spherical bodies. Meanwhile the nucleus as a 

 whole has elongated, and eventually becomes separated into two 

 parts in typical amitotic fashion. 



That nucleoli of somatic cells may stand in nutritional relation- 

 ship to the cytoplasm has been shown by the work of Schreiner 

 on Myxine (lo). He found that the oxyphil nucleolus or plasmo- 

 some of many of the somatic cells increased in size, became 

 lobulated, and portions broke away and passed in the form of 

 granules from the nucleus into the cytoplasm ; there they formed 



