I IO THE FROG 





brain, be careful to leave the investing membranes intact. 

 Fix in Zenker's fluid. Since the sections are to be used 

 merely for the general topography, the method of staining 

 is not important, and the borax-carmine Lyons-blue picric- 

 acid method is to be preferred on account of its rapidity. 

 Cut rather thick sections (io/x to 15^). 



19. Cross-sections of the auditory region. In toads, 

 and certain species of frogs, the young are small at the time 

 of metamorphosis. Secure such a specimen and fix the en- 

 tire head in Muller's or Tellyesnicky's fluid. Decalcify with 

 70 per cent, alcohol containing 10 per cent, nitric acid, and 

 stain in toto with borax-carmine or with paracarmine. Im- 

 bed in paraffin and cut rather thick sections; be careful to 

 orient the object in such a manner as to secure exactly trans- 

 verse sections, some of which will pass through the colu- 

 mella. 



20. Cross-sections of entire frogs. Obtain some 

 toads or small frogs recently metamorphosed, fix in Tell- 

 yesnicky's fluid, decalcify, stain in toto with borax-carmine 

 or with paracarmine, imbed in paraffin and cut the entire 

 body into thick transverse sections (15^ to 20 /^). As a re- 

 view exercise have students sketch sections taken at random, 

 and label the parts. 



