Eins Bell, BY 
in the medulla. Practically all the reticulum of both cortex and me- 
dulla, as well as the lymphocytes, are, therefore, of epithelial origin. 
The corpuscles of Hassall develop from the syncytium and are, there- 
fore, epithelial in origin. They are, however, not to be considered as 
remnants of the original epithelial anlage. 
In development various types of corpuscles are distinguished. The 
ordinary type of concentric corpuscles first appears as an enlarged clear 
nucleus around which colloid is being formed. Before or during the 
formation of colloid, the cytoplasm increases in quantity, filling the 
spaces of the reticulum and producing a centrifugal pressure which 
shapes the newly-formed colloid into concentric lamella and fiattens the 
neighboring nuclei, making them concave toward the center. The cen- 
tral nuclei usually become obliterated. 
The epithelioid type is distinguished by its resemblance to large epi- 
thelial cells, this appearance being due to the formation of colloid 
lamelle around large areas of clear cytoplasm. The central part of the 
corpuscle usually remains unchanged until after some of the colloid 
lamellee are formed. 
The cystic type differs from the ordinary type only in that the central 
part undergoes vacuolization instead of colloid transformation. Those 
with concentric vacuoles may simulate blood-vessels containing nucleated 
red cells. Corpuscles never contain erythrocytes; neither can they be 
injected at any stage of development. Serial sections also show that 
there is no connection to blood-vessels at any stage. 
Compound concentric corpuscles are formed by the union of two or 
more simple concentric corpuscles during development. 
Irregular corpuscles are not concentric in arrangement, and are 
formed in the syncytium in an irregular manner. In the compact type 
of irregular corpuscles, concentric areas may form. 
The formation of colloid is an essential feature in the development of 
every corpuscle, and is not to be considered as a process of degeneration. 
Since the conclusion of my work and after my manuscript was given to the 
publishers, two articles dealing with the thymus have appeared. 
Ph. Stohr (Ueber die Thymus, Sitzungsberichte der phys.-med. Gesellschaft 
zu Wurzburg, June 8, 1905) believes that the thymus first epithelial in nature 
becomes converted entirely into small cells of lymphoid appearance. Later 
the large reticulum cells are formed from these by enlargement. The cor- 
puscles of Hassall are formed by the massing together and enlargement of 
these lymphoid-like cells. The small round cells of the gland are epithelial 
in origin but are to be regarded not as lymphocytes but as epithelial cells. 
The thymus is not a source of lymphocytes. 
