xiii.] THE FROG. 263 



of connective-tissue bundles, running for the 

 most part parallel to the surface. 



j. The kidney. 



i. Take a frog's kidney which has been for a week 

 in solution of bichromate of potash, and then for a 

 day or two in spirit. Imbed it, cut sections parallel 

 to its flatter surfaces, and mount in glycerine. 



a. Examine with a low power. 



a. Note the numerous tubules of which the organ 

 is mainly composed and which twist about in 

 all directions, and are consequently cut, some 

 transversely, some obliquely, and others more 

 or less longitudinally. The absence of any 

 marked division into cortex and medulla. 



/?. The clear round holes, scattered about; these 

 are sections of glomeruli from which the con- 

 tained vessels have fallen out. Some may be 

 seen in which a granular mass still lies. 



b. Examine with a higher power 



a. The epithelium lining the tubules, composed 

 in some of granular and ill-defined cells, in 

 other (usually larger) tubules of clearer and 

 better-defined cells; both varieties are nu- 

 cleated. 



c. Examine specimens of injected kidney with a 

 low power. Note the vascular tufts of the glo- 

 merulL 



k. The testis. 



i. Imbed a testis which has been hardened in alcohol : 

 cut sections and mount in glycerine. 



