Chandler: A Lymphoid Structure in Lepisosteus 93 



found in these areas. It is further significant that the substance 

 stains exactly the same as the granules, red with eosin, and 

 yellow with picro-fuchsin. I cannot say that the granules do 

 pass into the vessels and disintegrate, but there is no positive 

 evidence against it, and there are some facts in favor of it. 

 Although the granules appear to be normal, the possibility exists 

 that they may be due to parasitism, or some other abnormality. 

 The masses of granules, from ten to twelve microns in diam- 

 eter, are held together by some membrane, probably a very thin 

 cell wall, but it is not evident in the sections. The granules are 

 sometimes scattered somewhat when the mass is cut across just 

 as are the melanin granules in the pigment cells. Associated 

 with each mass there is a fairly large nucleus which shows much 

 more plainly in some cases than in others (pi. 11, fig. 2). Due 

 to the lighter coloring of the granules with picro-fuchsin, the 

 nuclei show best with that stain. These granular masses are 

 found in varying density throughout the gland, except in the 

 open connective tissue network immediately behind and around 

 the cerebellum. In the main body of the gland they are scat- 

 tered in approximately the density shown in plate 11, figure 2, 

 though possibly on an average slightly more numerous. In the 

 ear-like projections, however, they are far more dense, so dense, 

 in fact, as to obscure all the other kinds of cells, and to conceal 

 the reticular network entirely. 



DEVELOPMENT 



Thinking that the origin and development of this gland-like 

 structure might throw some more definite light on its nature and 

 function, I sectioned a series of embryos ranging from 6 mm. 

 to 22 mm. in length. The heads of these embryos were stained 

 in toto in Delafield's haemotoxylin, imbedded in paraffin, and 

 cut in sections 10 microns in thickness. 



As the eosin counter-stain was the most effective with the 

 adult, this was likewise used for the embryos. 



Up to the 18 mm. stage there could be found no indication 

 whatever of any structure lying over the myelencephalon, the 

 ependymal lining of the brain cavity coming in close juxtapo- 

 sition to the cartilaginous roof of the skull, or lying immediately 



