they produce bodies of irregular shape — some 

 pointed, some rounded, and some multiangular. 



After the cell has developed about half of its 

 normal complement of rods, it is called a meta- 

 myelocyte up to the stage where, at maturity, it 

 has the full number of rods. This is a purely 

 arbitrary division and admittedly not exact, but 

 it would be still more difficult in avian blood to 

 follow the criterion "Bean or kidney shaped 

 nucleus" (Anonymous, 1949) because, with ap- 

 proaching maturity, the typical artifact of the 

 heterophil nucleus becomes apparent; therefore, 

 in figure 377 it would be impossible to say 

 whether this cell had an indented or bean-shaped 

 nucleus but it is quite evident that it has about as 

 many rods as the cell will hold. 



Figures 375 and 376 are examples of meta- 

 myelocytes. In both tliere are one or two ma- 

 genta rings still carried over to this late stage; 

 usually, of course, they have disappeared by this 

 time. From figure 376 it is obvious that mitosis 

 does not stop at the granuloblast stage or even 

 when the specific granules first appear. 



Developmental stages of eosinophils are as 

 scarce in the bone marrow as are the mature 

 forms in the circulating blood. The finding of 

 developmental stages went slowly but eventually 

 after enough cells had been studied certain defi- 

 nite features were established that helped to sepa- 

 rate them from heterophils. The qualities of 

 cytoi^lasm and nucleus that make the eosinophil 

 metagranuloblast distinguishable from the heter- 

 ophil of the same age have already been dis- 

 cussed in part. The nucleus of the eosinophil 

 throughout its developmental stages generally is 

 more intensely stained than that of the heterophil. 

 Usually the vacuoles are clear — almost refrac- 

 tile — but as shown in figure 378 a few faintly 

 stained bodies are visible. These differentiate 

 directly into the specific granules, and the meso- 

 myelocyte (fig. 379) shows a full scale of tinc- 

 torial range from the faintest to the darkest. It 

 is diis direct transition from seeming vacuole to 

 definitive granules that eliminated the promye- 

 locyte stage. There appears to be nothing equi- 

 valent to the magenta rings. 



In the heterophil the developmental steps of 

 the precursor spheres were moderately well 

 synchronized in their formation; whereas, in the 

 eosinophil, development of the spheres begins at 

 different times, so that all stages are present at 



any one time. Even in the older age (fig. 380) 

 the full range — vacuole to faint sphere to dark 

 sphere — is clearly shown and the framework 

 cytoplasm has the same pale-blue color that it has 

 in the adult cell. 



In the legend for figure 380 this cell is called 

 a mesomyelocyte, and this stage, as defined here, 

 is one that has less than half of its granules. At 

 first glance this cell appears to have half of its 

 granules, or more. But this cell and the hetero- 

 phil are dealt with in the same way — only those 

 granules are counted that have arrived at maturity 

 and have their full tinctorial density. On that 

 basis the cell definitely has less than half of its 

 granules. 



Had the late metamyelocyte (fig. 381) been 

 found in the circulating blood it would probably 

 have been counted as a mature cell — similar cells 

 from circulating blood, shown in figures 177— 

 180, have been so named. The difference is that 

 the cytosome of the cell in figure 381 was not 

 fully packed with granules. Wlien the eosino- 

 phil of the circulating blood was discussed, it 

 was pointed out that the specific granule for this 

 cell varied from a large homogeneous body to a 

 group of four small bodies in a cluster. At no 

 time have the small bodies been found in the de- 

 veloping stages of eosinophils in embryo spleen 

 or adult bone marrow. This variation is an im- 

 portant one, and will be discussed again when 

 the blood of ducks is described, but its significance 

 in the cytomorphosis of the cell is still unknown. 



Studies of basophil and eosinophil differentia- 

 tion are handicapped by the fact that so small a 

 proportion of cells belong to these groups. As 

 with the eosinophil it has been assumed that the 

 granuloblast stage of the basophil has the same 

 appearance as described for the heterophil. 

 Wlien cells like tliose in figures 366 and 367 are 

 found, there are no identifying cytologic land- 

 marks to indicate the direction in which they will 

 develop. It was not difficult to locate cells that 

 resemble those in figures 384-386, but cells like 

 figures 382 and 383 were classed at first as 

 heterophils because they showed magenta bodies. 

 Further study proved, however, that they were not 

 quite identical with those in the heterophils. In 

 the cells under study the magenta bodies were 

 predominantly granules ranging from small to 

 large; the large ring characteristic of the hetero- 

 phils was absent or relatively rare. There were 



196 



