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51 and 52 Basophilic myelocytes (medullary mast-cells). (Compare with 
ancestral cell, fig. 39, and circulatory mast-cell, fig. 12.) 
53 Earlier stage of medullary mast-cell with finer basophilic (deep blue) 
granules and a long pseudopod in process of constricting off a ‘platelet’ with 
basophilic granules. 
54 Young neutrophilic granulocyte. (Compare with the ancestral large 
lymphocytes, figs. 34 and 35.) The centrosome is conspicuous in the concavity 
of the reniform nucleus. The neutrophilic granules have not yet spread through- 
out the entire cytoplasmic mass; a relatively wide non-granular hyaline area 
appears at the left. 
55 to 59 Suecessively later stages in the development of the neutrophilic 
myelocytes. The polylobular nucleus may constrict to form a polynuclear cell 
(fig. 57); this amitotic division of the nucleus may in some cases be followed by a 
fission of the cytoplasm (fig. 59). These cells contain astralsy stems like those 
of the circulatory cells. 
60 Small polymorphonuclear neutrophilic myelocyte. (Compare with fig. 22, 
a polymorphonuclear neutrophilic leucocyte of blood of dog.) 
61 and 62 Young neutrophilic myelocytes with pseudopods. 
63 A neutrophilic myelocyte which has protruded four pseudopods into a 
capillary space of the marrow, a phenomenon duplicating that by which meg- 
akaryocytes of mammals pass platelets directly into the blood stream. 
64 to 68 Various forms of neutrophilic myelocytes with pseudopods which 
constrict to form typical platelets (fig. 65). 
69 Complex polymorphonuclear neutrophilic myelocyte arising directly from 
mesenchyme among a group of fat cells, two of which are indicated at the right. 
70 Similar neutrophilic myelocyte from the fatty mesenchyma. (Compare 
with fig. 24.) 
71 Plasma-cell from the medullary mesenchyma, a derivative from a large 
lymphocyte. (Compare with fig. 35.) 
72 and 73 Mononucleated giant-cells from the marrow mesenchyme. These 
are strictly comparable to the mononucleated hemogenic giant-cells of mammals, 
from which the polymorphonuclear giant-cells (so-called megakaryocytes), the 
source of blood-platelets, develop. These amphibian homologues of mammalian 
hhemogenic giant cells likewise possess a basophilic cytoplasm with metachro- 
matic (lilac colored) granules, and arise from hypertrophying hemoblasts. 
Segmenting pseudopods of such cells produce typical platelets. 
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