EXPLANATION OF PLATES 



All figures were drawn with the camera lucida at table level with Zeiss apochr. 

 imm. 1.5 mm. objective. For figures 1, 2, 7, 15, 18, and 22, Spencer ocular 10 was 

 used; the other figures were drawn with Zeiss comp. ocul. 12. Unless otherwise 

 stated, all figures were drawn from slides preserved with Bouin's fluid and stained 

 with iron hematoxylin. The plates were reduced one-third in reproduction. 



ABBREVIATIONS 



b, blood-vessel I, small lymphocyte 



d, dwarf hemocytoblast m, granulocytoblast 



e, endothelium s, cells of the sexual cords 



g, granulocyte t, transitional stages between the gran- 



h, hemocytoblast ulocytoblasts and granulocytes 



PLATE 1 



EXPLANATION OF FIGURES 



1 A portion of the medullary zone of the ovary in a Sebright embryo of the 

 eighteenth day of incubation, i, interstitial cells (lutear cells of Boring and 

 Pearl) almost entirely surrounding a germ cell; o, germ cells. Delaf. hematox. 

 eosin. 



2 Loose mesenchyme separating the testis from the Wolflfian body in the em- 

 bryo of the tenth day of incubation, h', extravascular hemocytoblasts. 



3 Endothelium of a capillary in the tenth-day embryo. One of the endo- 

 thelial cells, e', begins to increase in size to be transformed into a large cell, r, 

 erythrocyte. 



4 Two large endothelial cells almost entirely differentiated from the endo- 

 thelium of an artery. 



5 Large endothelial cell about to be detached from the endothelium of a capil- 

 lary. Figures 3, 4, and 5 were drawn from slides of the tenth-day embryo. 



108 



