274 SPLANCHNOLOGY. 



small apertures, or stomata, so that these sacs are now considered 

 as being depositories of lymph ; and " thus a continuity of 

 surface is established between the serous membranes and the 

 lining membrane of the blood- vascular system through the 

 lymphatics." — (Turner.) 



GLANDS. 



Without attempting an exhaustive definition of the glands, it 

 may suffice to state here that for the most part they are organs 

 in which is carried on the process of secretion, or separation from 

 the blood of certain matters, which may be required to assist in 

 the various vital functions, or may be destined to be speedily cast 

 off as effete or poisonous material. Most glands in their typical 

 structure resemble a mucous membrane, consisting of epithelial, 

 subepithelial, vascular, and nervous portions ; the first of these 

 portions usually rests upon a condensed layer of the second, 

 which is known as the memhrana iiropria, or basement mem- 

 brane. The vessels supply the gland with blood, from which the 

 secretion peculiar to the gland is separated by the vital 

 power of the cells, which power is stimulated by the nerves, the 

 latter also regulating the blood supply. Lymphatic vessels are 

 present, but their use in these organs is obscure. The sub- 

 epithelial tissue supports the other component structures of the 

 gland, at the same time determining its anatomical form. The 

 secretions of glands are, as a rule, discharged on the free surfaces 

 of the body — i.e., on the mucous membranes or skin — by means 

 of tubes known as the gland-ducts ; hence such glands may be 

 conveniently regarded as depressions in the mucous membrane or 

 in the skin. 



When a gland appears as a tube-like depression in the mucous 

 membrane it it termed a follicle, crypt, or simiole tubular 

 gland ; if the cavity is dilated, it is known as a sac, or saccular 

 follicle ; and if either of these forms be provided with secondary 

 recesses, it is said to be multilocular. A tubular gland may be 

 coiled upon itself; or it may branch, in which case it becomes 

 a compound tubular gland. A tubular depression ending in a 

 number of vesicular recesses constitutes a simple racemose 

 gland ; a compound racemose or conglomerate gland consists of 

 a number of simple ones with a common duct. 



The ductless glands form a group which differs from any of 

 the above in the absence of a duct, the secretion usually being 



