at figures 224, 233, and 234, which were selected 

 to show range in size and in nucleocytoplasmic 

 ratio. Mitotic figures are abundant at this age, 

 as shown by cell 16 in figure 224 A and cells 21 

 and 22 of B. For persons seeking a large tough 

 cell suitable for the study of the avian chromo- 

 somes, the writers know of no better material, 

 although they have not examined the neuroblast 

 that has been used so frequently. In smears 

 fixed in Petrunkevitch No. 2 and stained with 

 May-Gioinwald Giemsa it has been possible to 

 count about 60 chromosomes and it is likely that 

 some of the problems in this fiekl could be solved 

 with technics selected specifically for cytogenetic 

 studies. 



There is perhaps one word of caution to be 

 given. Cytologic evidence indicates that the 

 prime function of this generation of erythrocytes 

 is to form hemoglobin. This is accomplished in- 

 dependently of the differentiation stages that 

 usually accompany this process. As a result, 

 mitosis is often abnormal, and frequently chro- 

 mosomes lag behind in the anaphase stage. The 

 abnormalities observed at mitosis in the primary 

 generation of erythrocytes are similar to those 

 reported on mitosis in neoplastic cells. Abnor- 

 mally large size often occurs in neoplastic cells 

 and an occasional giant cell may be found among 

 primary erythroblasts (fig. 251) .^ Such mitotic 

 abnormalities and giant cells probably mean 

 little or nothing toward the production of later 

 blood neoplasias in the bird but since some em- 

 bryonic cells have certain points in common with 

 neoplastic cells, the possibility always exists that 

 a residual, dormant cell of this type, if not de- 

 stroyed, could later be stimulated to reproduce 

 itself. Most primary erythrocytes degenerate 

 along conventional lines, as seen in figures 249, 

 250. 252, and 253. 



Hemoglobin development proceeds very rap- 

 idly and by 65 hours incubation (fig. 225) has 

 reached the early and mid-polychromatic stages. 

 This terminology is based on the tinctorial qual- 

 ity of the cytosome and not on nuclear or cyto- 

 plasmic differentiation. On the basis of criteria 



'^Dawson (1933a) observed that giant atypical erj'throcytes 

 were produced in Necturus in the regeneration process that 

 followed a destruction of normal erythrocytes by lead poison- 

 ing. The occurrence of gigantism in mammalian erythro- 

 poiesis has been reviewed by Berman (1947). It may ex- 

 press itself as a large uninucleated cell, as shown here for 

 the chicken, or as a giant multinucleated cell. The latter may 

 undergo multipolar mitoses and Berman is of the opinion that 

 some of these may return to normal, uninuclear cells. 



usually applied to the human species, these cells 

 would still be called erythroblasts, since the term 

 "polychromatic" is applied to cells after the nor- 

 moblast stage has passed, but for the bird, the 

 usage followed here seems to give maximum uni- 

 formity of nomenclature for comparative pur- 

 poses with otlier species having nucleated red 

 cells. These terms — early, mid-, and late — re- 

 fer to the blue, gray, and orange phases of color. 

 As previously indicated, the blue represents a 

 predominant stroma of basophilic material. 

 The gray stage appears gray because there is a 

 mixture of two opposite colors — blue and 

 orange — and as more of the original Ijasophilic 

 stroma is lost, there is no longer a balance and the 

 orange color predominates. In later generations 

 of cells this transition is a period of cytosomal 

 weakness, and artifacts readily appear in poly- 

 chromatic erythrocytes. In the first generation, 

 however, the transition is so rapid that the cyto- 

 some does not develop a weakened condition; 

 hence artifacts are not commonly seen (fig. 225) . 

 Artifacts appear in some cells after they have 

 reached the late polychromatic stage (fig. 226). 

 Erythrocytes at 65 hours incubation have taken 

 on spherical shapes but they may be pressed into 

 angular shapes when the smear is made, and there 

 may l)e overlapping of cells that produces clear 

 bands and crescents in the cytosome (fig. 225, 15 

 with 17). 



The cytosome is closely packed with mito- 

 chondrial spaces that have undergone a change 

 from the rods of the earlier stage to innumerable 

 small granules Uiat give to the cytosome a tex- 

 turial quality, and would be inaccurate if a homo- 

 geneous wash of color were applied to the draw- 

 ings of these cells. 



A peculiarity of these cells is the presence of a 

 seemingly ectoplasmic mantle around the periph- 

 ery of some cells (figs. 225, 4, and 235), the 

 significance of which is unknown. Illustrations 

 of immature human red cells from various 

 sources have not shown anything similar to it. 

 This leads one to suspect that it may possibly be 

 an artifact associated with the large size of the 

 avian cell. A tendency toward the same type of 

 reaction is shown in some of the cells of figure 

 226 but this reaction does not reappear in any 

 of the later generations, nor do smaller cells of 

 the same age (fig. 236) show the marginal rim. 



At this age (altout 65 hours) the nucleoli, usu- 

 ally two in number, are even more distinct than 



117 



