PHYSIOLOGY OF THE NUCLEOLI 57 



II. MATERIAL AND METHODS 



As the material for this study, I used the larvae of the com- 

 mon cabbage butterfly, Pieris rapae Linn., and those of a large 

 caddis-fly, Neuron ia postica Walker. 



Usually the silk-glands were taken out by the decapitation 

 method before being placed in the fixing agent; sometimes a dis- 

 section in normal salt solution was made and the silk-g)ands 

 obtained by this method also proved to be as good material. 

 Some other specimens, especially of very young stages, were 

 fixed in toto. Flemming's chromo-aceto-osmic (strong formula) 

 and Hermann's platino-aceto-osmic mixtures were used with 

 good result for fixing the material. Gilson's mercuro-nitric also 

 proved to be a very good fixative. Sections were cut from 3 

 to 5 micra thick, and the majority of them were stained on the 

 slide with Ehrlich's triacid or Flemming's triple stains. A 

 number of other stains were tried to bring out the changes in the 

 staining reaction of the migrating nucleoli. 



III. OBSERVATIONS AND CONSIDERATIONS 



A. Morphological 



a. Pieris rapae Linn (Plate 1). The silk-glands of Lepidop- 

 tera have been studied by Helm ('76), Van Liadth de Jeude 

 ('78), Joseph ('80), Carnoy ('84), Blanc ('89), Gilson ('90), 

 Tanaka ('11) and Ito ('15) from different standpoints. More 

 cytological are the papers of Korschelt ('96, '97) and Meves 

 ('97), and especially the interesting cytological paper on the 

 process of silk-secretion by Maziarski ('11). 



In his earlier work, Korschelt ('96) noticed two stainable ma- 

 terials within the nucleus, and called them macrosomes and 

 microsomes. He described the former as large round, rregu- 

 larly angular, or spindle-shaped bodies, and the latter as small 

 particles which always stained darker than the former. The 

 macrosomes, according to this view, represent the chromatin, 

 and the microsomes are nothing but the nucleolar material. 



