SECRETION. 



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combine to form one cavity lined or filled with secreting cells which also 

 occupy recesses from the main cavity. The smallest branches of the 

 gland-ducts sometimes open into the centres of these cavities; some- 

 times the acini are clustered round the extremities, or by the sides of 

 the ducts: but, whatever secondary arrangement there may be, all have 

 the same essential character of rounded groups of vesicles containing 



Fig. 220. Plans of extension of secreting membrane by inversion or recession in form of cav- 

 ities. A, Simple glands, viz., 17, straight tube; h, sac; i, coiled tube. B, Multilocular crypts; fc, 

 of tubular form ; T, saccular. c, Racemose, or saccular compound gland ; m, entire gland, show- 

 ing branched duct and lobular structure ; n, a lobule, detached with o, branch of duct proceed- 

 ing from it. D, Compound tubular gland (Sharpey). 



gland-cells, and opening by a common central cavity into minute ducts, 

 which ducts in the large glands converge and unite to form larger and 

 larger branches, and at length by one common trunk open on a free 

 surface of membrane. 



Among these varieties of structure, all the secreting glands are alike 

 in some essential points, besides those which they have in common with 



