SPERMATOGENESIS OF LEPISMA DOMESTICA 383 



to eat. For moisture I have kept shallow dishes filled with 

 moist filter-paper in the Stenders. In spite of these precautions, 

 in the course of a month or so the creatures begin to show a 

 shrinkage of the abdominal region and soon die with the posterior 

 region shrunken fully one-half. 



The insects were either killed in xylol or decapitated and the 

 testes dissected out immediately in physiological salt solution. 

 As soon as the body cavity was opened, some fixing fluid was 

 introduced by means of a fine pipette. This renders the tissues 

 more opaque and makes it easier to locate the gonads which are 

 loosely surrounded by fat, as well as to cause better fixation. 



For counting chromosomes, Bouin's fluid at 38°C. proved the 

 best, but for general fixation of the cytoplasm as well as of 

 chromatic structures nothing equaled Flemming's strong solu- 

 tion. In addition, Hermann's fluid, Benda's Flemming, 10 

 per cent formalin, Allen's modification of Bouin, Petrunkevitch's 

 fluid, and Kopsch were tried out and had their special uses. 



The testes dissected out, fixed, washed, and dehydrated, were 

 imbedded in paraffin and cut into sections from 3 to 12 jx thick. 

 Sections of 7 /x thickness were found to be very satisfactory for 

 study, and in general this was the thickness used. 



The stain used generally throughout was Heidenhain's iron 

 haematoxylin without any counterstain. In addition, various 

 counterstains were tried, and also, in an effort to get a selective 

 stain for mitochondria, Benda's alizarin-crystal violet method. 

 A modification of Cajal's silver-impregnation method by Hortega 

 ('16), especially recommended for centrosomes, was given an 

 inadequate trial with but fair results. 



I have also examined a number of splended slides stained by 

 the safranin-gentian-violet-orange G method, for which I am 

 indebted to Dr. P. W. Whiting. 



