THE GONADS OF THE FOWL 95 



externa of the follicles. It is not so conspicuous in the so-called 

 theca interna. 



That the granulocytes thus produced recognize a mesenchymal 

 origin and are not derived from the blood is obvious on account 

 of the early stages in the transformation of the mesenchyme 

 cells into hemocytoblasts. Furthermore, no granulocytes could 

 be detected within the blood-vessels, even in the case of the 

 small capillaries. 



The occurrence of myeloid metaplasis in the mature bird points 

 to the existence of a stock of undifferentiated mesenchyme cells, 

 endowed with multiple potentialities. Under the influence of 

 unknown physiological stimuli, such unmodified cells may pro- 

 liferate, giving rise to hemocytoblasts which undergo the same 

 evolution as those present in the mesenchyme of the embryo. 

 As wdll be described in the following pages, the myeloid trans- 

 formation also affects tjie small lymphocytes which produce 

 acidophile granules in their cytoplasm and eventually change into 

 a smaller type of granulocytes. Danchakoff ('16 b, c) has 

 described a syncytium of mesenchyme cells in the nodules of 

 lymphadenoid tissue, where considerable numbers of small lym- 

 phocytes are produced. Elements with all the characteristics of 

 undifferentiated mesenchyme cells were found by the waiter both 

 in the testis and ovary of the adult bird. These cells persist in 

 the gonads during a long time, perhaps throughout the life of 

 the individual. They occur in the intertubular spaces and also 

 in the stroma of the ovary, and represent portions of the embry- 

 onic mesenchyme which have failed to change into fibroblasts. 

 The latter appear chiefly around the seminal tubules and ovarian 

 follicles. 



THE NATURE OF THE SO-CALLED INTERSTITIAL CELLS (BORING 



AND PEARL) 



The facts described in the preceding pages establish on a sound 

 basis the homology of the hematopoietic foci found in the mesen- 

 chyme of the gonads and those present elsewhere in the general 

 mesenchyme of the embryo. Special emphasis has been laid on 

 the transformation of the granulocytoblasts into granular leuco- 



