222 R. R. HUMPHREY 



methyl-green staining technique, and the modified Zenker's 

 fluid followed by dichromate mordantage and Weigert staining 

 as recommended by Kingsbury ('11) for the demonstration of 

 lipoids. In addition to the above, portions of the testis were 

 fixM in Benda's and Regaud's mixtures for the demonstration 

 of mitochondria. Regaud's IV B mixture was most used for 

 this purpose, fixation for twenty-four hours being followed by 

 mordantage in 3 per cent potassium dichromate solution for 

 two to three weeks, and staining by the Weigert method Fixers 

 less frequently employed were the mixtures of Hermann and 

 Flemming, Bouin's picro-aceto-formol, Carnoy's 6-3-1, con- 

 centrated mercuric chloride, 10 per cent formol, ordinary Zen- 

 ker's fluid, Helly's fluid, and copper dichromate-sublimate- 

 acetic. The testis of Necturus being an elongated organ, it was 

 ordinarily cut transversely into pieces of 2 to 5 mm. length for 

 fixation AA'hen studies of the organ indicated it possessed 

 cephalocaudal regional differences, testes were fixed entire, at 

 frequent intervals, and sectioned longitudinally in order that 

 such differences might be conveniently studied in a single prep- 

 aration. Frequently, also, when material was limited, and 

 studies of longitudinal sections fixed with a number of fluids 

 seemed desirable, the testes were cut in halves longitudinally 

 with a sharp razor instead of being fixed entire, a single animal 

 thus affording four portions, from each of which complete longi- 

 tudinal sections might be obtained. Serial sections were not 

 considered necessary. All sections were cut as thin as practi- 

 cable; for more detailed studies sections 3 to 6m thick were used. 

 In addition to this very complete series of Necturus material, 

 there has been available for comparative study material from 

 several other urodele amphibians. The series of testes of Des- 

 mognathus fusca was especially complete, including specimens 

 taken during every month of the year except January. The 

 greater part of this material had been fixed in Hermann's or 

 Flemming 's fluid and stained with iron hematoxylin. The 

 Diemyctylus viridescens material in the collection represented 

 animals killed in nine months of the year, and included testes of 

 the immature red land phase as well as those of the mature aquatic 



