boundary between it and the adjacent highly 

 vacuolated cytosome. 



Cells 7 to 10 show the preciusoi- spheres from 

 which develop the densely stained orange bodies. 

 In cell 7 they are barely visible as light orange 

 bodies from the vacuoles produced in the meta- 

 granuloblast stage. In cell 9 the spheres are 

 slightly more intensely colored. In cells S and 

 10 a few orange spheres are almost as darkly 

 stained as in the mesomyelocyte stage, but in 

 none of the four cells {7-10) have the orange 

 spheres taken on the deep eosin coloration that 

 precedes the elongation of a sphere into a definite 

 rod. Description would probably be facilitated 

 if names were given to the lightly and the darkly 

 stained orange spheres; when a thorough cyto- 

 logical and cytochemical study of rod produc- 

 tion has been made, logical names will suggest 

 tliemselves. 



Cell 12 of figure 330 is an erytlu'cblast and is 

 clearly identified by its typical structure as be- 

 longing to the blast stage of development. Such 

 cells are relatively rare at this age. Numerous 

 early polychromatic erythrocytes are pi'esent. 

 Cells 13 and 14 are examples; so is the cell lo- 

 cated between 3 and 4. Cells i5 to 17 are ex- 

 amples of mid-polychromatic erythrocytes, and 

 cells 18 to 21 of late polychromatic erythrocytes. 

 There are cells in the field other than those desig- 

 nated by number; they also belong to these vari- 

 ous groups. Mitosis, at least in the embryo, can 

 take place in late polychromatic eryljirocytes 

 (cells 23-27) and, of course, at earlier stages 

 of development also (cell 22). It would be in- 

 teresting to follow the plasmosome nucleolus 

 during mitosis and note how it is reconstituted 

 during the interkinetic period, but the technics 

 used here are not suitable for such a study. 



Thrombocytes are less common in smears from 

 hematopoietic organs than from circulating blood 

 and it may be that this is due to the delay in open- 

 ing the embryo and dissecting out the organ be- 

 fore the smear is made. It is quite possible that 

 in fixed and sectioned material some thrombo- 

 cytes undergo degeneration and become cells that 

 resemble small lymphocytes or naked nuclei. A 

 reinvestigation of thrombocyte development from 

 stained sections might help to clarify the stages in 

 thrombocyte differentiation. Cell 29 (fig. 330) 

 is a thrombocyte of medium size and looks some- 

 what like figure 289, except that the chromatin is 



less clumped. Typical small thrombocytes are 

 shown in the cells numbered 30 in figure 330. 



Smudged cells are present in every smear and 

 usually are more numerous than the one example 



shown in figure 330, 31. 



BLOOD CHANGES AT HATCHING 



During the 24 hours after the hatching of the 

 chicks dramatic alterations occur in the circulat- 

 ing blood, spleen, and bone marrow. The most 

 complete change appears in the spleen, where a 

 general outpouring of heterophils is followed by 

 a massive development of lymphocytes and mono- 

 cytes. Within several days following hatching 

 the bone marrow becomes an organ that produces, 

 predominately, erythrocytes, thrombocytes, and 

 granulocytes. No extensive series of illustra- 

 tions covering these events has been prepared, 

 chiefly because in any period of rapid transition 

 what may be seen at one moment in one chick 

 may be entirely different in another. 



Notes were taken on smears from a group of 

 chicks ranging from a few hours to several days 

 after hatching. The actual protocol taken at the 

 time probably tells the story as well as a more 

 studied rewrite of the same thing. We recom- 

 mend a similar study to anyone who has attained 

 some proficiency in cell identification and is 

 grasping for a feeling of the dynamics of develop- 

 ment and balance as it occurs hidden from our 

 usual vision. 



Throughout this transition period there was 

 considerable variability between birds and it 

 would be necessary to use a larger number of 

 chicks at each age to determine the exact typical 

 sequence of events. At each period usually four 

 chicks were used. 



1 TO 3 HOURS POSTHATCHING 



Circulating blood. — Only in an occasional chick was 

 the number of white blood cells anywhere near a nor- 

 mal ratio; in most cases, the number was definitely be- 

 low normal. This was especially true in regard to the 

 lymphocytes, monocytes, and basophils. The predom- 

 inant cell in the early chick blood, just after hatching, 

 is the heterophil. The other cells come into the picture 

 at a later age. Even the heterophil, immediately after 

 hatching, may be absent from the blood (fig. 230). 

 Immature stages of erythrocytes are usually present. 



157 



