GENERAL HISTOLOGY: STRUCTURE OF ORGANS 37 



in the cavity of the gland, which now appears larger than in the resting condition; 

 the cells in the inactive condition are smaller, cuboidal, with centrally situated 

 nuclei. Intermediate states, of course, occur between these two extremes. 



The poison glands are much larger than the mucus glands and of infrequent 

 occurrence except on certain parts of the skin. There may be none on your 

 slide. The epithelial cells form a very thin layer surrounding the very large 

 cavity, and frequently the cell walls are not distinct. The secretion, which is 

 poisonous, appears as granular masses near the epithelium. 



Each of the glands is invested with a thin layer of smooth muscles, and outside 

 of this a layer of connective tissue. Neither of these layers can be clearly made 

 out in the preparations. 



c) The stratum compactum: This consists of a dense layer of white connective 

 tissue fibers, arranged parallel to the surface of the skin. At intervals, vertical 

 strands, consisting of connective tissue, smooth muscle cells, blood vessels, 

 nerves, etc., cross the wavy layers of the stratum compactum at right angles, 

 and may extend up into the epidermis. 



d) The subcutaneous connective tissue: Beneath the stratum compactum 

 occurs loose connective tissue which is not a part of the skin but forms the 

 boundaries of the subcutaneous lymph sacs. 



Draw a portion of the skin, showing in detail the structure of all the layers. 



E. STRUCTURE OF THE KIDNEY 



Examine slide "Frog kidney" (see Holmes, pp. 202-6). The section is 

 taken across the kidney. The flattened surface is ventral; the rounded surface 

 dorsal. In the middle of the ventral surface, observe a yellowish or orange mass, 

 the adrenal gland, made up of masses of epithelial cells (this is not present on all 

 sections) ; and in this region also there are usually seen sections of large arteries 

 and veins. The two sides of the kidney may be distinguished in section as 

 follows: the outer edge is more pointed and contains cross-sections of a large 

 vein, the renal portal vein, and the ureter. 



1. The tubules. The greater portion of the kidney is made up of extremely 

 long tubular glands, called tubules, which are much coiled and twisted. Because 

 of this coiling, the tubules appear in section as circles, ellipses, crescents, etc. 

 Each tubule possesses a large and distinct central cavity, and its wall consists 

 of a single layer of cuboidal epithelial cells, whose function is to extract the 

 nitrogenous waste matters from the blood. Note the numerous blood vessels 

 between the tubules, and the connective tissue between the tubules and covering 

 the surface of the kidney. 



2. The Malpighian bodies or renal corpuscles. Each uriniferous tubule 

 begins in a Malpighian body, little rounded masses situated near the ventral 

 surface. Examine one of these with the high power. It consists of a dense tuft 



