8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



seen, even under this low magnification. The diameter of the gland 

 is so small that but few lobules are to be seen in any one cross section. 



Figure ii (pi. 2) represents a small portion of the section shown 

 in the previous figure as seen under a magnification of about 400 

 diameters. The gland is, of course, made up chiefly of the small, 

 darkly-staining lymph cells (Ic) which vary to some extent in size 

 and shape but are mostly spherical. Their nucleus is densely granular 

 and occupies practically the entire cell. No signs of mitosis, men- 

 tioned by Vincent (11), were seen in these cells. The reticulum 

 supporting the lymph cells seems to be made up of small, angular 

 cells (re) with long fibrillar processes, extending between the adjacent 

 cells. Scattered among the lymph cells are numerous capillaries (ca) 

 in many of which erythrocytes (cr) are to be seen, and in some, 

 leucocytes (hi). 



Irregular lymph sinuses (Is) may also be seen, sometimes contain- 

 ing large, finely granular cells. Occasional large cells (er) stained 

 strongly with eosin, are apparently merely stray erythrocytes from 

 some adjacent blood vessel. 



The Hassall's corpuscles (he) are numerous and varied in size and 

 appearance. A rather large one is shown at the upper left of the 

 figure, a smaller one to the right of this. The larger one is perhaps 

 the more typical. It shows a central group of very small, dark cells, 

 surrounded by a granular mass in which there are a number of 

 elongated or crescentic cells exhibiting a fairly distinct concentric 

 arrangement characteristic of Hassall's concentric corpuscles. Many 

 of these corpuscles are so small that the characteristic structure can- 

 not be made out. 



THE SPLEEN 



The spleen in the alligator has about the usual appearance and 

 location as is seen in other animals, though perhaps of rather small 

 relative size. For example, in a 40 cm. animal the spleen was an 

 elliptical body, 8 mm. in its long, and 4 mm. in its short diameter. 



A low-power sketch through such a spleen, at right angles to its 

 long axis, is shown in plate 2, figure 12. The capsule (e) is well 

 developed but varies much in thickness. It consists of a fairly distinct 

 inner and denser layer and a less dense outer layer in which blood 

 vessels are often seen ; between these two layers large blood spaces, 

 filled with blood, are often seen. 



One of the characteristics of the alligator spleen, at least in the 

 material studied, is the almost complete absence of trabeculae extend- 



