I48 ELEMENTARY BIOLOGY. [CHAP. 



c. The cutaneous glands. Look for thin sections 

 which pass through their necks. 

 «.. The gland; usually lined by a single layer of 

 flattened epithelial cells (more rarely by two 

 diversely differentiated ones) occasionally sur- 

 rounded by pigment. Its secretory product 

 may often be seen within it, as a pale finely 

 granular mass. 



/?. The duct ; subdivided into two segments : an 

 inner enlarged one, lined by a single layer of 

 cells which graduate into the deeper layer of 

 the epidermis ; an outer much constricted 

 one, the epithelium of which graduates into 

 the horny layer of the epidermis. 



y. Look for sections showing the glands en face. 

 Note the boundaries and characters of their 

 epithelial cells. 



16. The intestine. 



i. Preserve some pieces of the small intestine, first 

 washing out the contents with care, in \ per cent, 

 solution of chromic acid; transfer to alcohol of 

 increasing strengths; stain with borax-carmine, 

 imbed and cut transverse sections. Mount in 

 Canada balsam and examine with a low power. 



a. The intestinal wall ; smooth externally, much 

 folded internally. Its outer layer; uniformly 

 thick (muscular layer) : its inner layer ; much 

 folded and more deeply stained {epitheliuni). 



b. Examine the thinnest portion under a higher 

 power. Work from without inwards ; there will 

 be found in the order of enumeration — 



a. Serous layer (peritoneum) ; obvious as a faint 



