THE HISTOGENESIS OF DENSE LYMPHATIC TISSUE 199 



the relation between the epitheHal cells and the lymphocytes is 

 not definitely known. The lymphocytes rarely, if ever, pass 

 through the epithelium into the intestinal lumen. 



5. The granulocytes (eosinophilic) as found in the region of 

 the intestinal tonsils are of two types, 1) blood eosinophiles, 

 wandering into the connective tissue from the blood stream, and, 

 2) connective-tissue eosinophiles, being derived in situ by differ- 

 entiation of lymphoid hemoblasts. 



The granules of the connective-tissue eosinophile are endog- 

 enous formations. They appear first as round bodies, later 

 changing to a rod-like form. The formation of granules is pre- 

 ceded slightly by loss in the basophilic character of the cytoplasm. 

 No change in staining reaction of the granules during the course 

 of their development was noted. Nuclear changes follow those 

 of the cytoplasm. The nucleus first becomes smaller and finally 

 divides into two, the binucleated condition being, apparently, 

 the adult condition. 



6. Granulopoiesis is most active in animals infected with para- 

 sites, as Coccidia. It also occurs most abundantly in and about 

 the caecum, where there may be assumed to be a constant irrita- 

 tion due to the presence of fecal matter. It may be suggested, 

 then, that inflammatory conditions may be associated with a 

 granulopoietic reaction. 



7. Extravascular erythropoietic foci occur in abundance at 

 certain stages in the development of the lymphatic tissue. These 

 are extravascular throughout their entire development, at no 

 time being within the blood vessels. No groups of lymphoid 

 hemoblasts or megaloblasts were found intravascularly at any 

 time of development. These erythroblastic cells also arise by 

 diff'erentiation of lymphoid hemoblasts. 



8. It is evident that conditions associated with the develop- 

 ment of the three types of blood cells are closely interrelated, 

 all being doubtless in some manner associated with the vascular 

 supply. The initiation of lymphopoiesis is apparently brought 

 about by some influence of the abundant lymph vessels or the 

 lymph upon the mesenchyme. The formation of nodular lym- 

 phatic tissue may possibly be controlled by the nutritive condi- 

 tions furnished by the blood supply. The further differentiation 



