THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 169 



It is also apparent that there are also two sources of origin for 

 the lymphoid hemoblasts; first, by direct transformation of larger 

 mesenchymal cells and, secondly, by growth of small and medium- 

 sized lymphocytes, which have previously been formed from the 

 mesenchyme. 



These facts are added evidence to the view held by several 

 authors (Maximow, Weidenreich, and Downey, etc.) that small 

 and large lymphocytes (lymphoid hemoblasts) are not distinct 

 cell forms, but merely difffrent growth stages of the same cell, 

 there being here a growth cycle, the small lymphocytes, by 

 growth, becoming lymphoid hemoblasts, and the latter, by re- 

 peated divisions, forming small lymphocytes. 



Because of the characteristic wheel-like arrangement of nu- 

 clear material in the small lymphocytes (which arrangement is 

 not as characteristic of small lymphocytes in the rabbit as in 

 some other forms), one is inclined to regard them as a definite cell 

 form. The difference in the appearance of the nuclei of the 

 two forms is, however, partially explained by the crowding to- 

 gether of the nuclear material into smaller area, which would 

 also tend to obscure a nucleolus, if such were present. 



But in case it is accepted that small lymphocytes and large 

 lymphoid hemoblasts are different growth stages of the same cell 

 form, it must be remembered that the cell as found in the small 

 lymphocyte stage possesses different potentialities than when in 

 the lymphoid hemoblast stage. The small lymphocyte may 

 produce, by division, others of its kind, or by growth, a lymphoid 

 hemoblast, which is the limit of its potentialities. It cannot pos- 

 sess the potentiality of producing other cells of the blood series 

 without first development and growth into a lymphoid hemoblast 

 (i.e., a small lymphocyte will never produce directly a granulo- 

 or erythroblast without, first, growth into a lymphoid hemoblast). 



In studying the relations causing or associated with the forma- 

 tion of lymphatic tissue, it is found that this tissue always de- 

 velops in places where there are rich lymphatic plexuses, and 

 also in close relationship with the blood capillaries.. These re- 

 lationships were noted by Gulland ('94), Saxer ('95), and Sabin 

 ('04) in developing lymphatic nodes. Hartmann ('14) decided 



THE AMERICAN JOURNAL OF ANATOMT, VOL. 29, NO. 2 



