302 ALWIN M. PAPPENHEIMER 



Very frequently, these cells contain one or more rounded cav- 

 ities, and in some cases the cell is composed merely of a shell 

 of striated fibrils, enclosing a single- large central cavity. In 

 one such cell observed in a living culture, the cell, which in its 

 free condition had taken on a globular form appeared to be 

 tunnelled by a cavity the rim of which was slightly more refrac- 

 tile and presented a distinct striation. The nucleus was appar- 

 ently located in a lobular projection at one portion of the cell. 



Two views are held as to the nature of the myoid cells, — one 

 supported by Mayer (3), Pensa (4), Weissenberg (5), and others, 

 that they are derived from muscle fibers which become included 

 in the gland in the course of its development; the other sup- 

 ported by Hammar (6) and Pappenheimer (7), that they are 

 modified elements derived from the reticulum. In sections, the 

 appearances lend countenance to the latter view: fibrils may 

 occasionally be traced from one cell to another and transitions 

 between reticular cells and cells with poorly developed fibrils 

 apparently occur. In teased preparations, these elements may 

 be readily recognized by their large size, regular contours, 

 refractile appearance, and by the presence of striations some- 

 times seen on careful focussing. They appear always under 

 these circumstances, as sharply circumscribed, usually globular 

 bodies, so that we must assume that their anatomical connec- 

 tion with the reticular syncytium, is extremely slight. Their 

 capacity for migration and growth in plasma cultures, is also 

 nil. They show no amoeboid activity, but retain their fixed 

 form, accumulate fat and gradually degenerate, in marked con- 

 trast, as will be pointed out later, to the reticular elements. 

 Evidence of contractility on the part of the fibrils was carefully 

 looked for, but an abrupt change of form suggesting such a 

 function, was not observed. 



In sections, the reticular cells are differentiated from the 

 small thymic cells principally by the character of their nuclei, 

 which are larger, paler with a more distinct chromatin network. 

 The outlines of these cells are indistinct, the cells forming a loose 

 protoplasmic meshwork in the interstices of which lie the myoid 

 cells and the small thvmic elements. In the cortex, amongst 



