100 JOSE F. NONIDEZ 



namely, a small nucleus surrounded by a thin layer of cytoplasm ; 

 the nucleus contains chromatin blocks located in its periphery 

 and lacks a plasmosome (fig. 22, I). The small lymphocytes are 

 formed in the mesenchyme surrounding the blood-vessels and 

 also in certain places which later become lymphatic nodules, 

 arising from cells which agree in their characteristics with the 

 elements called dwarf hemocytoblasts by Danchakoff, who 

 described these cells in the spleen of the chick ( '16, d). The dwarf 

 hemocytoblasts either differentiate into large hemocytoblasts or 

 into small lymphocytes. Although in the spleen both kinds of 

 elements'are at first separated, in the gonads and adjoining organs, 

 they appear side by side in the same lymphogranulopoietic focus 

 (fig. 15, t', l).^ 



The formation of small lymphocytes in the mature gonads may 

 be very active under certain physiological conditions, leading in 

 some cases to a lymphoid metaplasis of the connective tissue. 

 One of these cases has been represented in figure 22, drawn from a 

 section of the regenerating testis in an adult Campine cock. 

 Large areas of the intertubular tissue are occupied by an enor- 

 mous number of small lymphocytes and small-sized hemocyto- 

 blasts. Transitional stages are also found in large numbers. 

 Some of the mesenchyme cells have become large hemocytoblasts, 

 but the latter do not develop acidophile granules in their cyto- 

 plasm and exhibit a marked tendency to divide by amitosis. 

 Once produced, the small lymphocytes migrate toward the blood- 

 vessels and eventually penetrate into their lumina to be carried 

 by the blood to other regions of the body. They appear in large 

 numbers within the veins, but could not be detected in the 

 arteries. Their migration into the latter seems to be prevented 

 by the thickness of the endothelium in these vessels and also by 

 the fibroblasts surrounding the endothelium. 



The most important point in connection with the presence of 

 small lymphocytes in the gonads is their transformation into 

 several types of cells which sometimes occur in the connective 

 tissue separating the seminal tubules in mature birds. While 

 some of these cells can be easily identified as modified lymphatic 

 elements, there are others, however, which closely resemble the 



