88 JOSE F. NONIDEZ 



vascular hemocytoblasts become granulocytoblasts after depo- 

 sition of acidophile granules in their cytoplasm, and transitional 

 stages in this evolution may be found in the same microscopical 

 field (fig. 15). Thus a complete series can be established from 

 an early stage in which no granules have appeared in the 

 cytoplasm to a condition in which the granules are very abun- 

 dant and the nucleus has lost its round outline to form a 

 crescent-shaped structure which may break into several portions. 



After the fifteenth day of incubation small lymphocytes begin 

 to appear in the mesenchyme. They are also formed in the hema- 

 topoietic foci and in special lymphopoietic areas which become 

 lymphatic nodules. Besides the myeloblastic and lymphatic 

 elements, there are usually in the clusters formed by both kinds of 

 cells elements endowed with a high phagocytic capacity. The 

 origin of these cells, which closely resemble the hemocytoblasts, is 

 obscure. They play an important role in the resorption of the 

 granule-laden cells present in the hematopoietic foci, which are 

 rarely found in the newly hatched and young chicks. 



Hematopoietic foci similar in all respects to those mentioned 

 above were also found in the Wolffian bodies (fig. 15), metane- 

 phroi, suprarenal glands, developing epididymis, and in the mesen- 

 chyme surrounding all these organs. They also occur in the 

 ovarj^ and corresponding organs in the female, showing the same 

 morphological features as those present in the testis. Finally, 

 they were also detected in the loose mesenchyme of the limbs in 

 a ten-day embryo. In all these cases they appear in close 

 proximity to the blood-vessels, in regions occupied by undifTer- 

 entiated mesenchyme cells. 



If we turn to the literature, we can find that hematopoietic 

 foci have been reported in the chick by several observers, espe- 

 cially by V. Danchakoff ('08 a, b; '16 b, c), who has made a 

 careful study of them in her researches on the origin of blood in 

 the hematopoietic organs and mesenchyme of different regions of 

 the body. 



Firket ('14) has mentioned the presence of granule-laden cells 

 in the ovary of embryos from the twelfth to the eighteenth day 

 of incubation. According to this investigator, who recognizes 



