there is some evidence for it in birds, such as 

 shown in figures 2, 12 and 13; 3, 12; and 6, 7, 

 8, 17, and 29. Some indentations extend rather 

 far into the nucleus and sometimes there are two 

 completely separate nuclei in the cell. Figure 

 29 demonstrates fairly clearly that a cell with 

 two nuclei such as shown in figures 7 and 8 can 

 be derived by constriction of a single nucleus 

 and not by mitosis in which the cytosome failed 

 to divide. Figure 17 is an early stage in the 

 process of nuclear constriction. Cells A and B 

 of figure 29 were from chickens used in an irradi- 

 ation experiment. The history of the birds that 

 furnished these cells is given in the legend. 

 Neither of these two cells can be considered nor- 

 mal, but in B the cytosome is partly divided and 

 even though abor-tive, as it obviously is in this 

 cell, fulfills some of the criteria for amitosis. 



Charipper and Dawson (1928) believed that 

 the erythrocytes of amphibians, which showed 

 the same range of morpliological variations found 

 here in chickens, offered evidence for the occur- 

 rence of amitosis. As already discussed, cells 

 with two nuclei or cells with constricted cyto- 

 somes (figs. 34, 35, and 36) may be found in 

 avian blood, but the same two processes have 

 not yet been found in the same cell except in 

 figure 29 B and in a primary erythrocyte (fig. 

 246). The idea of amitosis would be more 

 convincing if one could find series of stages in 

 which the nucleus was first involved and divided 

 into halves and each half moved to opposite poles 

 when the cytosome divided. Tlie point will be 

 discussed again when artifacts are considered. 



Developmental stages found in circulating 

 blood (figs. 9-28) 



Cells more immature than reticulocytes are so 

 rare in the circulating blood of the normal, 

 healthy mammal that the presence of even an 

 occasional one in a smear is suggestive of a 

 padiological condition. In avian blood the pres- 

 ence of immature erythrocytes is common and 

 as far as we know now, an occasional immature 

 cell does not indicate a blood dysfunction. Im- 

 mature stages are found in birds of all ages, and 

 three birds that were over 5 years of age con- 

 tributed examples of polychromatic erythrocytes 

 in the series of figures presented here. If one 

 seeks stages earlier than polychromatic erythro- 



cytes, considerable searching is necessary, but 

 even erytliroblasts so immature that they might 

 be classed as large lymphocytes have been found 

 (figs. 9 and 10). 



Since blast cells of various sorts and poten- 

 tialities have close morphologic similarity among 

 themselves and in turn resemble what has been 

 called a large lymphocyte, it seemed best as far 

 as circulating blood is concerned to discuss them 

 under the subject of lymphocytes, and four ex- 

 amples have been illustrated (figs. 121-124). 

 Some differential counts given in the literature 

 would indicate that large lymphocytes were pres- 

 ent to the extent of 1 percent and over. This 

 must be a different cell from the one described 

 here since the "large lymphocytes" observed in 

 these studies occurred so infrequently that they 

 would not be included in a differential count. 

 Further amplification of the point will be made 

 later (p. 50), but figure 121 has the character- 

 istics that identify it as an erythroblast and thus 

 could be included among the series of develop- 

 mental stages shown in figures 9-23. A dis- 

 cussion of other structural features that distin- 

 guish an erythroblast from other blast cells is 

 given on page 9. 



When development has reached the stage of 

 an early polychromatic erythrocyte, there is no 

 longer confusion with other cells, and typical ex- 

 amples are shown in figures 11 and 12. Mito- 

 chondrial spaces may or may not be present in 

 the cytosome, and cells at this stage of develop- 

 ment have not as yet acquired the homogeneity 

 of cytoplasm that comes later. Sometimes the 

 cytoplasm is vacuolar as shown in basophil eryth- 

 rocytes from bone marrow (figs. 348 and 349). 

 In figure 11 there is a faint suggestion of a 

 nucleolus near the lower nuclear margin. The 

 term "erytlnoblast" has been reserved for the 

 early stages of development where a nucleolus 

 is present, yet in the red-cell line the nucleolus 

 may still be visible at the early polychromatic 

 stage and in the primary generation of the em- 

 bryo, even to the mid- and late stages. The 

 early polychromatic erythrocyte often has been 

 called a basophil erythroblast, but actually some 

 hemoglobin has already been acquired at this 



stage 



The polychromatic phases of erythrocyte de- 

 velopment are represented by cells in which the 

 cytoplasm possesses an affinity for both baso- 

 philic and acidophilic dyes in various propor- 



24 



