126 



CHORDATE ANATOMY 



secreting area; but those of the axillae are branched and greatly enlarged. 

 They are of the "vitally secretory" type, that is, the cell protoplasm 

 merely produces the secretion, but is not converted into it, and the cell 

 continues alive indefinitely. The sweat is usually oily but, in man, 

 becomes watery under the influence of the nerves. See Fig. 117. 



ASSOCIATION 



NEURONE 



EFFERENT NERVE 



SWEAT GLAND 



CAPILLARIES 



Fig. 117. — A diagram illustrating the nervous mechanism of temperature regulation 

 in man. The quantity of secretion of tubular glands (and consequently the amount 

 of sweat which may evaporate to cool the body) depends upon the quantity of blood in 

 the capillaries associated with the glands and dermal papillae. Through a reflex arc the 

 circulation is regulated by the temperature of the skin. (Redrawn after Hough and 

 Sedgwick.) 



Sebaceous Glands. Sebaceous glands in man occur on most parts 

 of the body, but are wanting on the palms and soles. Most hairs have 

 sebaceous glands connected with their follicles. 



They are of the acinous type, and necrobiotic, that is, their protoplasm 

 forms the fatty secretion, which the cell extrudes, and then dies. 



Other Glands. Besides the sebaceous and sweat glands, there are 

 other highly specialized cutaneous glands, the lacrimal glands of the eye 

 and the Meibomian of the eyehds, the wax glands of the auditory meatus, 

 besides preputial, vaginal and anal glands, which occur in most 

 mammals, and mammary glands in all mammals. 



Of the organs which have evolved from glands, none are more sur- 

 prising than the luminous organs or photophores of deep-sea fishes. These 

 are true dark lanterns since they have a condensing lens and a reflecting 

 membrane. The light is produced by the oxidation of luciferin secreted 

 by the gland. No carbonic acid and little heat are evolved in the process. 



