THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 181 



the production of lymphocytes (Briicke, '51; Hartmann, '14). 

 In view of the fact that lymphatic tissue develops in places of 

 degenerating body material, such as degenerating glands, rudi- 

 mentary organs, etc., many authors thought the tissue as de- 

 veloping in these places assisted in absorbing and doing away 

 with this degenerating material (GuUand, '91; Stohr, etc.). 

 Still others noted some relationship in the intestinal tonsils 

 between the intestinal glands and the formation of lymphatic 

 tissue, but were not sure of the nature of this relation (Flesch, '88; 

 Klaatsch, '92). 



It is well known that, in the presence of regressive structures, 

 mesenchymal, or embryonic connective tissue shows a 4ympho- 

 cytopoietic' reaction. Accumulations of lymphocytes are en- 

 countered in glands of various kinds, as kidney, thyroid, salivary 

 glands, minor digestive glands, etc., these accumulations being 

 accompanied by degeneration and infiltration of certain of the 

 glandular acini (Kingsbury, '15). Stohr also calls attention 

 to the fact that 'leucocytes' collect in places where organs are 

 degenerating, as the pronephros of lower forms, gills of anura, 

 thymus, processus vermiformis. 



In the case of the rabbit, it is quite clear that the degeneration 

 of any structures in the region of the intestinal tonsils does not 

 initiate the formation of lymphatic tissue there. For no crypts 

 of Lieberkiihn are formed until lymphopoiesis is well underway. 

 However, as the nodules of lymphatic tissue increase rapidly in 

 size, they often include in their midst portions of intestinal glands, 

 which are usually degenerating, this degeneration probably due to 

 the infiltration of the lymphocytes, rather than the opposite. 

 Any association observed here between the crypts of Lieber- 

 kiihn and the lymphatic nodules is accidental, being due to the 

 very rapid growth of the lymphatic tissue. 



If the lymphatic tissue were to be interpreted as a lympho- 

 cytopoietic reaction of mesenchjrnie to regressive or degener- 

 ating structures, these structures must have been present at some 

 time in the ancestral history, which in the animal, as existing now, 

 do not appear at any time in its development. 



