TISSUES OF THE BODY. 347 



ponding to these, three forms of glands, which are, however, liere and 



Fig. 330. Simple tubular 

 glands from the mucous 

 membrane of the human 

 stomach. 



Fig. 331. A convoluted 

 gland from the con- 

 junctiva of the calf. 



Fig. 332. The vesicles of 

 a racemose gland (Brun- 

 ner't) from the human 

 being. 



there blended one into another, and also make their appearance at one 

 time as simple, at another as very complex apparatuses. 



(1.) In the first form (fig. 330) the envelope 

 presents itself as a narrow passage of very variable 

 length, almost always closed at one end and open 

 at the other, discharging itself either indepen- 

 dently or in connection with other structures of 

 the like nature in the form of a very complex 

 apparatus. An envelope of this kind is known 

 as a gland tubule, and such glands are named"* 

 tubular. Of these two kinds are recognised, 

 namely, the simple, where the whole organ con- 

 sists entirely of one microscopically small sac ; 

 and the complex, where several or very many of 

 these tubuli are combined to form a new anato- 

 mical unit, or if we prefer another view, where 

 the tubules are sub-divided. They may even form 

 a retiform combination of tubes. If the latter 

 attain great length, as is the case in two com- 

 pound glands of the human body, the testicle and 

 the kidney, they may be regarded as a special 

 variety under the name of gland tubes (fig. 333, a-e). 



Fig. 333. Branching urni- 

 ferous tube from the kidney 

 of a kitten, a-e, progressive 

 subdivision at acute angles. 



