ZOOLOGY 



Glands 



Excretion 

 and secre- 

 tion 



ness and reason we appear to transcend all rational 

 explanation ; the intellect, powerful though it may be, 

 cannot understand itself. It is better frankly to admit 

 our ignorance than to clothe it in words which sound 

 learned but mean little. 



7. Gland tissue, consisting of the cells secreting the 

 saliva, gastric juice, sweat, etc., is a modified form of 

 epithelium, in which the functional significance is en- 

 tirely altered. These cells, like many of the connective 

 tissue group, take up material from the blood, and from 

 it produce special substances according to the kind of 

 gland. The closed cavities of the body are lined with 

 glandular epithelium, secreting serum. The largest 

 gland in the body is the liver ; developing from a pocket 

 or depression in the wall of the alimentary canal, it as- 

 sumes great complexity, both in external features and 

 minute structure. The pancreas and kidneys are also 

 glands, but the latter serves to excrete waste products 

 from the blood, instead of producing a substance to be 

 subsequently utilized. Physiologically speaking, secre- 

 tion and excretion are not essentially different ; but in 

 the former case the product is utilized, in the latter it is 

 waste. 



