PLATE 1 



EXPLANATION OF FIGURES 



1 Rabbit, age five days. To show the position of the first masses of free 

 cells appearing in the region of Peyer's patch. Photo X 180. 



2 Rabbit, age nine days. To show the consistency of these masses. With 

 the exception of one lymphoid hemoblast, all shown are of the small lymphocyte 

 type. Photo X 750. 



3 Rabbit, age thirty-two days. A portion from the center of an intestinal 

 lymphatic nodule of Peyer's patch. Note how loosely packed the cells are here 

 as compared with the peripheral portion of the nodule (fig. 4), also the scarcity 

 of mitotic figures. 



4 The same as figure 3. From the peripheral portion of the nodule. The 

 lymphocytes of both types are very densely packed here. Mitotic figures are 

 numerous. 



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