FO&MS OF GLANbS. 191 



ways so that a wide surface can be packed in a small bulk, 

 just as a Chinese paper lantern when shut up occupies 

 much less space than when extended, although the actual 

 area of the paper in it remains of the same extent. In a 

 few cases the folding takes the form of protrusions into the 

 cavity of the secreting organ, as indicated at (7, Fig. 40, but 

 much more commonly the surface extension is attained in 

 another way, the supporting or basement membrane, cov- 

 ered by its epithelium, being pitted in or involuted as at B. 

 Such a secreting organ is known as a true gland. 



Forms of Glands. In some cases the surface involutions 

 are uniform in diameter, or nearly so, throughout (Z?, Fig. 

 40). Such glands are known as tubular; examples are 

 found in the lining coat of the stomach (Fig. 48); also in 

 the skin (Fig. 76), where they form the sweat-glands. In 

 other cases the involution swells out at its deeper end and 

 becomes more or less sacculated (E}\ such glands are named 

 racemose or acinous. The small glands of the skin which 

 form the oily matter poured out on the hairs (p. 273) are 

 of this type. In both kinds the lining cells near the deeper 

 end are commonly different in character from the rest; and 

 around that part of the gland the finest and thinnest walled 

 blood-vessels form a closer network. These deeper cells 

 form the true secreting tissue of the gland, and the tube, 

 lined with different cells, leading from the secreting re* 

 cesses to the surface on which the secretion is poured out, 

 and serving merely to drain it off, is known as the duct of 

 the gland. When the duct is undivided the gland is simple; 

 but when, as is more usual, it is branched and each branch 



What is a tubular gland? Examples? A racemose gland? 

 Example? Where do we find the closest network of blood-vessels 

 in a gland? Which cells of a gland make its secretion? What is 

 meant by the " duct" of a gland? What is a simple gland? 



