THE FROG 105 



gills during the period of their early and rapid development. 

 Those species whose larvae contain little pigment (e. g., 

 Cryptobranchus, Desmognathus or Necturus) are best. Fix 

 the entire embryo or larva in Flemming's solution or in 

 Carnoy's mixture; mount small pieces of the epidermis on a 

 slide and stain with Delafield's hsematoxylin. The peri- 

 toneum of salamander larvae is said to furnish good material ' 

 for the study of mitosis. 



Dividing cells are especially numerous in the early stages 

 of maturation of the germ cells in the salamander testis. 

 The material must be secured at the proper season of the 

 year, which must be determined for each species. Fix the 

 entire testis in Tellyesnicky's fluid or in Carnoy's mixture, 

 cut transverse sections and stain on the slide with iron 

 hsematoxylin and Bordeaux red. 



7. Striated muscle fiber. Fresh material, used as de- 

 scribed in the text, is best, bur since this may not always be 

 available it is well to have on hand some small pieces of 

 muscle killed in 10 per cent, formalin and preserved in 5 per 

 cent, formalin. Fiber preserved in this way is good to show 

 striations, but does not respond to the action of acetic acid 

 to demonstrate the nuclei; the latter may be stained with 

 Delafield's haematoxylin. 



8. Non-striated muscle fiber. After ligaturing the 

 intestine of a freshly-killed frog, inflate the bladder with 

 normal salt solution and place the entire specimen in Zenker's 

 fluid. After the material is well hardened cut the bladder 

 into small pieces, mount them on slides and stain with Dela- 

 field's haematoxylin; destain in acid alcohol and counter- 

 stain with picric acid. The mesentery may also be used to 

 show non-striated muscle fiber. Pin the intestine on a piece 



