CHAPTER XV. 



THE DUCTLESS GLANDS. 



THE organs included in this group possess, at some stage of their 

 development or in the adult, a structure analogous to that of the 

 secreting glands. Those which retain this structure after complete 

 development differ from the other glandular organs in being devoid 

 of ducts, through which the materials elaborated by their paren- 

 chyma could be discharged. Of these organs the thyroid is the most 

 striking example. Other members of this group, notably the thy- 

 mus, become greatly modified as development advances, and after a 



FIG. 154. 



Section of human thyroid gland : a, alveolus filled with colloid ; b, alveolus containing a 

 serous fluid ; c, interalveolar areolar tissue ; d, tangential section of an alveolus, giving 

 a superficial view of the epithelial cells. 



while retain mere vestiges of their original epithelial character ; 

 the chief bulk of the organ being composed of lymphadenoid 

 tissue. 



The following organs and structures will be considered as belong- 

 ing to the general group of ductless glands : the thyroid gland, the 



ISO 



