TISSUES OF THE BODY. 



355 



proper conception of a gland, and even in cases in which the latter pos- 

 sesses an outlet, there may be as yet no trace of a special canal for the 

 carrying oft' of the secretion of the part. 



All simple follicular glands belong to the latter order, in which the 

 form of cell changes just before 

 the outlet is reached, but the ter- 

 mination of the follicle itself is not 

 clearly defined. In those cases 

 only in which several of the latter 

 are united in one common, short, 

 and widened terminal portion, 

 can we speak of such a canal, 

 as in those peptic glands of the 

 stomach, in which the portion 

 common to the several tubules 

 (Stomach cell of Todd and Bmv- 

 man) is marked by the difference 

 of its columnar cells (fig. 347, a). 

 The straight portion of the tubules 

 of convoluted glands may be 

 looked upon as an excretory duct, 

 as it passes from the convolu- 

 tion toAvards the outlet, although 

 neither the structure of the wall 

 nor the cellular lining is altered in the least ; the diameter, however, 

 decreases at first. On the other hand, among complex tubular glands, 



Fig. 345. Network of vessels in the rabbit's liver. 



Fig. 346. From the thyroid of the infant, a, crypt of 

 gland filled with cells alone ; b, incipient colloid meta- 

 morphosis of the contents; c, the latter far advanced ; 

 d and/, large lymphatics; , small lymphatics. 



Fig. 347. A compound peptic gland 

 from the dog. a, wide orifice of exit 

 (stomach celt) clothed with columnar 

 epithelium; 6, point of division; c, 

 single follicles lined with peptic cells; 

 rf, contents passing out. 2. The orifice 

 (a) in transverse section. 3. Section 

 through the several glands. 



such as the kidney, we find an elaborate system of excretory ducts lined 



