EPITHELIAL AND ENDOTHELIAL TISSUE. 349 



and still larger ones, representing globular, nucleated plastids. 

 Simultaneously with this recurrence of the embryonal condition, 

 even in children, many of the lymph-corpuscles perish and are 

 transformed into a homogeneous, viscid, so-called colloid sub- 

 stance, which, in thyroid bodies of adults, is almost invariably 

 found in the closed spaces, now termed alveoli. The lymph-cor- 

 puscles are often arranged in the shape of a wreath along the 

 wall of the alveolus, and irregular clusters of these corpuscles are 

 found scattered throughout the colloid mass. The stages of 

 transformation of the plastids into the colloid substance can easily 

 be traced. (See Fig. 147.) 



FIG. 147. THYROID BODY OF ADULT. 



F, connective-tissue frame, carrying numerous blood-vessels; L, lymph-corpuscles: C, 

 colloid mass. Magnified 500 diameters. 



The connective-tissue capsule of the thyroid body sends 

 numerous prolongations into its depths, which constitute the 

 walls of the alveoli. A striking feature of this formation is the 

 great number of blood-vessels and lymphatics which penetrate 

 its interior. The significance of this body is, however, not under- 

 stood. 



The suprarenal capsule is composed of two layers a cortical 

 and a medullary layer. In the former we see radiating rows of 

 polyhedral bodies, having the appearance of epithelia, which 

 often contain fat- granules. The connective tissue throughout 

 this body is an offspring of the outer capsule, and is seen between 

 the rows of the polyhedral bodies j near the boundary line of the 

 cortical layer it forms a delicate reticulum, characterized by a 



