blast. None of these were found at any of the 

 ages examined, and the same was true for lympho- 

 blasts, monoblasts, and immature and mature 

 plasma cells. 



Immature and mature lymphocytes were found 

 at 285 hours, and appeared at all ages after 

 hatching. No monocytes were found in this 

 survey until after hatching. 



The heterophil is the dominant granulocyte and 

 is present at all ages and the incidence of granulo- 

 blasts just before hatching (481 hours) is higher 

 than after hatching. The data in table 10 indi- 

 cate that this is true also of the other immature 

 and mature stages of the heterophil. The same 

 tendencies are indicated in the eosinophils, where 

 tliey were found most abundantly at 347 and 481 

 hours incubation age; after hatching they re- 

 mained at a fairly low level. Perhaps the same 

 tendency is indicated also in the basophils but 

 the number of cells counted was too small to defi- 

 nitely establish a picture of a prehatching rise. 



Among miscellaneous cells, some primary 

 erythrocytes were obsei-ved at 285 hours and none 

 after that. This cell is one that is known to arise 

 in the yolk sac; therefore it was probably brought 

 into the bone marrow through the embryonic cir- 

 culation. 



Osteogenic activity was indicated at 285 hours 

 but none later except perhaps immediately after 

 hatching, and the fact that the elongated reticular 



cells were found only at these same two ages is 

 probably due to more than chance. Two macro- 

 phages were included in the counts at 285 hours 

 and again at 8 days after hatching, but it would 

 be expected that this cell might be seen at any 

 Mitosis for all types of cells was 1 percent 



age 



or less. The number of squashed cells fluctuated 

 irregularly. Cells that could not be identified 

 were most abundant at 285 hours. Following 

 that there was a downward gradient until the per- 

 centage reached a level of 0.2 at 4 days 18 hours, 

 and a level of 0.4 at 8 and at 175 days. 



In respect to cell counts the data presented here 

 differ greatly from those presented by Burmester, 

 Severens, and Roberts (1941). They found 

 large numbers of lymphocytes, whereas we found 

 only a few. The data by Forkner (1929) for the 

 adult chicken show some differences from that 

 given in table 10. Our data show a higher heter- 

 ophil than eosinophil count, whereas Forkner's 

 values have the reverse order. He did not in- 

 clude thrombocytes in his tabulation. His 

 lymphocyte count was considerably higher than 

 ours. 



Marvin (1954) calculated the total number of 

 bone marrow cells in both femurs and both tibia 

 in a strain of young White Carneau pigeons. His 

 mean normal value on 4 pigeons was 10*'X32±5 

 cells for the total marrow of these four leg 

 bones. 



199 



