14 MYELOID METAPLASIA OF THE EMBRYONIC MESENCHYME. 



nective-tissue cells elements bearing a peculiar and definite structure "interstitial 

 cells" were observed. Their morphological features were worked out in detail, 

 especially in the testes of mammals, including man. Peculiar inclusions in the form of 

 Reinke's crystals and riziform bodies, a characteristic structure of their idiosomes, 

 as well as the presence of numerous fat droplets, were demonstrated. An attempt 

 was also made to find homologous cells in the ovary. 



The data concerning the presence of similar cells lose much of their precision 

 in the observations made on the stroma of the sex-glands in lower animals. While 

 in mammals, including man, the interstitial cells were traced through early embry- 

 onic periods, their presence in birds, particularly in the chick, was questioned by 

 some investigators, not only in the embryo but also in the adult, and again asserted 

 by others. The more general criterion upon which interstitial cells were identified 

 in the chick consisted in most cases in the presence of numerous small fat droplets 

 in their cytoplasm. 



A parallel between the development of interstitial elements and of secondary 

 sex characters was reported, and an important function was attributed to them, 

 their secretion being assumed to be the factor determining the development of 

 secondary sex characters. In view of the importance of such an assumption, no 

 effort should be spared in securing additional data concerning these elements and 

 in pointing out occasional and sometimes unavoidable errors. 



The data concerning the presence of interstitial cells in the sex-glands of the 

 chick are still very contradictory. They were not found by Boring in the testes of 

 cocks from 1 to 12 months old (1912), in contradiction to de Cilleuls (1912), who 

 found them at this stage and also seemed to have established a direct relation 

 between the development of these cells and the sex characters of this animal. 

 Recently (1915) Reeves confirmed the presence of interstitial cells in the testes of 

 cocks 3, 5h, and 18 months old. 



In an effort to settle this question finally, Boring and Pearl once more took it up 

 and reported in their last paper (1917) that both in ovaries and testes interstitial cells 

 can be found; in the ovaries, as a regular constituent of the stroma; in the testes, 

 however, only occasionally in the newly hatched males. This observation was 

 made on material fixed in Gilson with Mann's and Mallory's stains. It was con- 

 sidered by the authors that the acidophilic granules demonstrated by this method 

 in some of the stroma cells of the sex- glands furnish a better criterion for the secret- 

 ing function of these cells, consequently of their "interstitial" nature, than the 

 presence of fat droplets. The illustrations which accompany this paper show free 

 cells with acidophilic round granules in their cytoplasm irregularly disseminated in 

 the stroma of the sex-glands. The presence of these cells recognized by the authors 

 as "interstitial" was found to be not regular enough to warrant the assumption of 

 such an important functional activity as the one ascribed to the interstitial cells 

 of mammals. 



Cells very similar to those described by Boring and Pearl were, however, 

 found by Danchakoff (1908) developing in the loose connective tissue of the chick 

 embryo. The presence of similar cells in the connective tissue in the adult chick 



