MYELOID METAPLASIA OF THE EMBRYONIC MESENCHYME. 17 



nature as wandering cells; a great variability is commonly observed in the number 

 of wandering cells in any part of the organism. 



.Even more striking are the changes occurring in the stroma of the testes; here 

 a few granular cells were found by Boring and Pearl only in newly hatched chicks. 

 A glance at figure 4 will show a great number of acidophilic granular cells developed 

 in the stroma of the testis of a chick embryo of 13 days. The changes in the stroma 

 developed in 5 days after grafting. At this stage the stroma of the normal testis 

 does not contain any granular cells; now and then a free wandering cell may be 

 encountered, but seldom, if ever, do these differentiate further under normal con- 

 ditions. The changes illustrated in figure 4 are therefore striking. At this stage 

 the organ is traversed by the testis cords, which consist for the most part of a 

 double row of cells, but which have not yet acquired a lumen. Large germ-cells, 

 very much like those seen in the ovary, are situated in the cords, but only a few of 

 them occupy a central position. 



If it were not for the presence of numerous free cells the stroma would be rather 

 poor in cellular elements, being, as a matter of course, composed of ordinary loose 

 mesenchyme. The numerous amoeboid cells make it, however, appear dense and 

 heavy. It is not my purpose to describe again the histogenesis of these cells. As 

 elsewhere, their source is the loose mesenchyme. 



There is a marked difference between the character of the granular cells in the 

 testes and those of the ovary, as shown in figures 4 and 5. The latter organ contains 

 numerous granular leucocytes, together with their earlier developmental stages; in the 

 testes most of the granular cells belong to the stage of granuloblasts. Their light 

 nucleus is spherical, sometimes horseshoe-shaped, and contains one or two baso- 

 philic nucleoli. In almost all the cells the acidophilic granules in the cytoplasm 

 are round ; only single cells can be found which approach the final stage of differentia- 

 tion into a granular leucocyte with rod-shaped granules. This difference depends 

 upon the fact that the two specimens were fixed at different stages— the ovary 8 

 days and the testes 5 days after the grafts were made. The granuloblasts, already 

 very numerous in the testes, had not yet had sufficient time to develop into their 

 final product, the granular leucocytes. 



The data given by Boring and Pearl concerning the regular presence of granular 

 cells in ovaries of the hatched chick may be looked upon as an indication of the 

 possible retention by the ovarian mesenchyme of its granuloblasts potency. The 

 mutual correlation of ovarian mesenchyme and germ tissue may leave the granu- 

 loblast^ potency of the mesenchyme of the ovary unaffected and in the presence of 

 proper stimuli its mesenchyme may respond by further more or less extensive 

 differentiation. Contrary to what is seen in the ovary, the authors did not find 

 acidophilic granular cells in the testes; the mesenchyme here is scarce in the grown 

 animal, but the absence of acidophilic granular cells certainly can not be interpreted 

 as an indication of a permanent loss by the testicular mesenchyme of its granulo- 

 blast^ potency. This may be the case, but it may also be that a proper stimulation, 

 capable of revealing in the mesenchyme its granuloblasts potency, is lacking here. 

 In embryos of 8 days of incubation, however, the mesenchyme of both the testes 



