8 LILLIE. [Vol. X. 



unstained, in a mixture of equal parts of glycerine and water. 

 As the water evaporated it was replaced with pure glycerine. 

 In the course of two or three days, in successful cases, the 

 eggs became so beautifully transparent as to show every detail 

 of structure with the most perfect clearness. In such prepara- 

 tions every nucleus, whether resting or in any of the stages of 

 mitosis, stood out conspicuously. It was thus possible to 

 follow all the divisions of the cells ; and I can state that I have 

 seen every spindle, up to a stage containing over fifty cells, 

 more than once, and most of them many times. 



Another method that may prove useful to others, and which 

 I have used with success, is to kill in Perenyi's fluid and 

 preserve the material in fifty per cent glycerine. Schneider's 

 acetic carmine may be used for staining in this case. 



For later stages Merkel's fluid is a splendid reagent. Cor- 

 rosive sublimate also gave excellent results. For staining, 

 Grenacher's borax carmine and Mayer's haemalum were used 

 chiefly. Good whole mounts in glycerine of young larvae were 

 obtained after the use of one tenth per cent, or even five hun- 

 dredths per cent, osmic acid. To kill the glochidia with the 

 shells open, I first added chloral hydrate to the water containing 

 them, and, in due time, any desired killing reagent. 



In all the earlier stages sections of the eggs were made e7i 

 masse, and no difficulty was experienced in orienting sections 

 thus made. It is a simple matter to orient the glochidium 

 before sectioning. In hard paraffine (58° C.) the shell of the 

 glochidium is no obstacle to sectioning. 



(c) Nomenclature. 



One of the practical questions which presents itself to the 

 student of cell-lineage is the system of nomenclature to be 

 adopted for the individual blastomeres. The requirements 

 are: (i) a separate designation for each cell which will in- 

 dicate its approximate location and exact ancestry in the 

 plainest possible way, and (2) the system must be capable of 

 indefinite expansion. These requirements sound difficult, and 

 the fact that so far no two workers have adopted the same 



