16 MYELOID METAPLASIA OF THE EMBRYONIC MESENCHYME. 



nothing to do with blood-forming activity. It was the merit of Swift (1914, 1915) 

 to have recognized in these cells the germ-cells. It is difficult to say whether the 

 germ-cells found in the ovary at a stage of 16 days of incubation (fig. 5) are still on 

 their way toward the already organized layer of germinal epithelium, or whether 

 they have already been cut off from it by the mesenchyme. I leave this question 

 undecided as not directly related with the present problem. The germ-cells found 

 at this stage in the stroma of the ovary are rather scarce and isolated, but are 

 accumulated in great numbers in the layer of the germinal epithelium. 



As above stated, these cells are not the only ones found free in the meshes of 

 the extremely loose mesenchyme in the developing ovary. Huge accumulations 

 of amceboid cells densely infiltrate the mesenchyme. Only a few of them do not 

 contain acidophilic granules, most of them being heavily loaded with round and 

 rod-shaped granulations. The amceboid cells, free from granules, are typical 

 lymphoid hemoblasts (hemogonia, stem-cells, mesamceboid cells). Innumerable 

 transitional stages clearly illustrate their gradual transformation into typical 

 granular leucocytes with rod-shaped granulation. As is usual in centers with a 

 sudden intensive manifestation of granuloblastic activity, the process of differentia- 

 tion loses its normal regularity and cells may be found in which the granulation 

 acquires the shape of rods at an early stage of its development; or, on the contrary, 

 cells with polymorphous nuclei still retain a round-shaped granulation. Also, 

 numerous small cells with round or oval nuclei and with numerous tiny acidophilic 

 granules in their cytoplasm may be observed among the granular cells. These 

 seem to be cells just detached from the mesenchyme, elaborating the granulation 

 without having passed through the stage of the large basophilic hemoblast. The 

 more diffuse accumulations of granular cells in the stroma of the ovary, as well as 

 those accumulated in the form of heavy coats around the arteries and veins, belong 

 undoubtedly to the series of the hemopoietic granuloblastic differentiation. The 

 granuloblastic metaplasia of the stroma in the ovary forms merely a part of the 

 general process involving the whole mesenchyme of the embryonic organism, at 

 least at this stage (7 to 8 days). 



Figures 12 and 13 of plate 4 illustrate, under low and high power respectively, 

 the granuloblastic metaplasia of the ovarian mesenchyme. They remove all possi- 

 ble doubt as to the authenticity and extent of the process. 



Are these huge accumulations of granuloblastic tissue found in the ovaries of 

 the host after grafts of adult spleen on its allantois in any way comparable to those 

 cells with acidophilic granulation found by Boring and Pearl in the ovary of the 

 normal hen? A close comparison of a series of preparations shown to me by Dr. 

 Boring with my own convinced us both of their similarity. I deeply appreciate 

 the courtesy shown by Dr. Boring in demonstrating her preparations for the pur- 

 pose of elucidating an unsettled question. The enormously increased granulo- 

 blastic activity in the ovarian tissue of embryos under experiment facilitated the 

 interpretation of the isolated mature cells encountered in the normal ovaries. 

 That Boring and Pearl did not always find these cells in the stroma of the sex-glands 

 and that when present their number varied might well be accounted for by their 



