SECRETING GLANDS. 



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glands (Fig. 686, E). In the compound tubular glands the division of the primary 

 duct takes place in the same way as in the racemose glands, but the branches 

 retain their tubular form, and do not terminate in saccular recesses, but become 

 greatly lengthened out (Fig. 686, F). The best example of this form of gland is to 



FIG. 686. Diagrammatic plan of varieties of secreting glands. A. Simple gland. B. Sacculated simple gland. 

 . Simple convoluted tubular gland. D, E. Racemose gland. F. Compound tubular gland. 



fae found in the kidney. All these varieties of glands are produced by a more or 

 less complicated invagination of a secreting membrane, and they are all identical 

 in structure ; that is to say, the saccules or tubes, as the case may be, are lined 

 with cells, generally spheroidal or columnar in figure, and on their outer surface 

 is an intimate plexus of capillary vessels. The secretion, whatever it may be, is 

 eliminated by the cells from the blood, and is poured into the saccule or tube, and 

 so finds it way out through the primary invagination on to the free surface of the 

 secreting membrane. In addition, however, to these glands, which are formed by 

 an invagination of the secreting membrane, there are some few others which are 

 formed by a protrusion of the same structure, as in the vascular fringes of synovia! 

 membranes. This form of secreting structure is not nearly so frequently met 

 with. 



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