THYMUS. 



171 



cytes in the thymus and their origin from entoderm are of great interest. 

 That the thymus cells are lymphocytes, however, is denied by Professor 

 Stohr who regards the cortex as composed of round entodermal cells de- 

 ceptively similar to lymphocytes, and as forming a degeneration zone of 

 thymus tissue. Of true leucocytes in the thymus he says, "In the places 

 where the medulla is directly in contact with the surrounding connec- 

 tive tissue and such places become constantly larger and more numer- 



Vein. 



Connective tissue. 



Thymic corpuscle 



K 



Entering. Medullary 

 leucocytes substance. 



FIG. 193. PART OF A SECTION OF THE THYMUS OF A CHILD AT BIRTH. X 50. 



ous as the organ grows many leucocytes wander into the medulla; they 

 lie in the connective tissue surrounding the medulla but not in that 

 around the cortex (Fig. 193)." Still another view is that the cortex 

 consists of reticular tissue of mesenchymal derivation, containing lym- 

 phocytes arising like those in lymph glands. The original entodermal 

 pouch is thought to become surrounded by dense mesenchyma and to form 

 but an insignificant part of the medulla. The nature of the thymus then 

 must still be considered obscure. 



