I.] THE FROG. 153 



y3. The smaller blood-vessels. In those immediately 

 related to the glomeruh, longitudinal and trans- 

 verse striations are generally obvious under the 

 above treatment. Examine with care; the longi- 

 tudinal stri^ will be seen to be the deeper 

 (boundary lines of epithelial cells); the trans- 

 verse ones are more superficial (boundary lines 

 of unstriped muscle cells). 



d. Compare sections of injected kidney. Examine 

 under a low power ; two sets of capillary vessels 

 will be seen — 

 a. Around and among the tubules. 



/). The glovieruli ; vascular tufts indenting the 

 Malpighian capsules (cf. h. /j). Examine them 

 in detail. 



20. The testis. 



Imbed a testis which has been hardened in alcohol 

 of increasing strengths and stained with borax-car- 

 mine. Cut into transverse sections and mount in 

 Canada balsam. 



a. Examine with a low power. 



a. The organ is chiefly made up of large tubules, 

 radially disposed at the periphery, more tortuous 

 internally. 



Spermatozoa may or may not be present ; 

 if so, they will probably be aggregated into 

 bundles with their heads (deeply stained) in 

 close relation with the walls of the tubules. 



b. Examine with a high power. 



a. Note the epithelium {germinal epithelium) lining 

 the tubules : it varies with the season of the 



