152 ELEMENTARY BIOLOGY. [CHAP. 



a. Examine with a low power. 



u. Note the numerous uriniferous tubuies of which 

 the organ is mainly composed ; they twist about 

 in several directions, and are consequently cut, 

 some transversely, some obliquely, and others 

 more or less longitudinally. The latter are most 

 conspicuous at the outer (convex) border. 



p. The clear round spaces, scattered about ; these 

 are sections of Malpighian capsules. Some may 

 be seen to lodge a granular mass (glomerulus). 



b. Examine with a higher power — 



a. The epithelium of the tubules ; composed for the 

 most part of a single layer of large squarish 

 cells, each with a large round- deep-staining 

 nucleus. 



jS. The epithelium of the capsules ; flattened and 

 squamous, its nuclei well defined, seen to be 

 reflected over the glomeruli (i. e. the latter are 

 outside it). Look for sections showing the con- 

 nection of tubules with capsules. 



y. Blood capillaries ; scattered among the tubules, 

 conspicuous in borax-carmine preparations by 

 the refractive deep-staining nuclei of the red 

 corpuscles (cf. § 18. b. y). 



c. Compare sections of the fresh kidney treated with 

 silver nitrate, as directed at § 2. c. Examine under 

 a high power. 



u.. The capsules. The boundary lines of their epi- 

 thelial cells will be distinctly seen; they are 

 those of a tesselated epithelium. 



