

XIII.] THE FKOG. 253 



77. Immediately beneath the epidermis is a thin 

 stratum of connective tissue in which lie many 

 large pigment-cells, sometimes forming an 

 almost continuous layer. 



6, Then come a large number of round cavities, 

 the cutaneous glands, lined by large, pale, 

 slightly granular, nucleated cells, which are 

 columnar when seen sidewise, but polygonal 

 when seen from the base or apex. Sometimes 

 the duct of the gland can be traced running 

 from it through the epidermis. Separating the 

 glands and supporting the epithelium are 

 bundles of connective tissue, consisting mainly 

 of fibres running perpendicularly to the sur- 

 face. 



i. The deepest layer of the dermis is made up of 

 connective-tissue bundles, running for the most 

 part parallel to the surface. 



j. The kidney. 



1. 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. 



