SECKETIONS. 



79 



called ampullary follicles, are met with in the simplest form, 

 under the skin of certain fishes, and seem also to form the 

 odoriferous glands found in the human integuments. When 

 grouped around a common branched secreting canal (Fig. 51), 

 they form the greater number of the composite glands, such 

 as the liver and salivary glands of mammals, and are named 

 by anatomists, Conglomerate Glands. 



156. The tubular-formed secreting organs present also 

 differences analogous to those just described. These tubes vary 

 infinitely in size, but are all closed at one extremity, and open 

 at the other for the escape of the excreted matter ; their varied 

 arrangements are seen in the glands under the integuments 

 in fishes, and in the bilious vessels 

 of some of the lower animals ; in 

 the pancreatic cceca, surrounding 

 the duodenum in fishes; in the 

 gastric glands of several birds; 

 finally, these same tubes (Fig. 52) 

 may acquire an extreme length 

 without change in their calibre, 

 clustered or heaped on themselves, 

 to terminate in an excretory tube, 

 but little ramified at its origin, in 

 such a way as to form a conglo- 

 merate gland, such as the kidneys 

 and other glands of great impor- 

 tance : some glands have a reser- 

 voir placed in the course of the 

 excretory duct, intended to per-, 

 mit of the accumulation of the 

 secretion, and its residence therein 

 for a time. The gall-bladder 

 (Fig. 24) and the urinary-bladder, 

 (Fig. 53) are pouches of this 

 nature. 



157. The imperfect glands 

 vary still more in their mode of 

 conformation. Some are composed of small closed cells, 

 isolated or agglomerated; others, called vascular aan- 



* A, vertical section of a kidney. a, cortical substance ; b, tubular sub- 

 stance ; c, calyx and pelvis ; d, canal of the ureter. 



B, intimate structure of this gland. , terminal portion of the urinary 

 tubes ; b, medullary portion of these same tubes : c, their termination in the 

 calyx. 



Fig. 52. Structure of 

 the Kidneys.* 



