THE LYMPHATIC SYSTEM. j-- 



mass appearing also similar to the earliest stage of a glandular area ; 

 repeated division rapidly converts the at first simple cylindrical aggre- 

 gation into a complex figure, in which an elongated main part bears 

 numerous lateral branches. At a later period the surrounding meso- 

 derrn becomes richer in cells and more compact and grows into the 

 original epithelial structure, the result of which invasion is the final 

 complete atrophy and disappearance of the epithelial constituents, 

 with the exception of the inconspicuous but constant corpuscles of 

 Hassall, which alone bear witness to the primary epithelial nature 

 of the organ. 



