BLOOD AND BONE-MARROW OF FROG 449 
by Niegolewski!® for Rana esculenta. We are in like disagree- 
ment with Niegolewski regarding the basophilic granules of the 
mast-cells. Nor is there any evidence that the original eosino- 
philic granules of the myelocytes have a nuclear origin, nor any 
that they have an extracellular origin, as claimed by certain 
investigators, e.g., Weidenreich.2t The eosinophilic granules 
arise gradually within the cytoplasmic area, apparently as a 
result of some specific activity of this protoplasm. 
Coincident with the above-described changes in the granules, 
the nucleus also passes through a series of structural and slight 
tinctorial alterations. At first the nucleus is approximately 
spherical, centrally located, contains a distinct plasmosome, and 
is vesicular in character (figs. 44 to 48). It gradually moves 
excentrically, meanwhile showing a coarser network and more 
numerous karyosomes, and a modification in shape leading 
through a reniform to a polylobular, and eventually, in some 
cases a multiple, character. Only the younger forms with 
spherical or stoutly reniform nucleus are seen in miototic divi- 
sion. In common with all myelocytes, including the lympho- 
cytes, these cells also form pseudopods which may constrict and 
fragment to form free ‘hyaline bodies’ (fig. 36) or, very rarely, 
globules with eosinophilic granules. Pseudopod formation and 
segmentation seem to be a common property of leucocytes, both 
circulatory and medullary. 
4. The development of the basophilic leucocytes. 'The basophilic 
leucocytes or mast-cells likewise take origin from the common 
lymphocyte progenitor, of medium size, in the extravascular 
tissue (figs. 38, 39 and 51). The nucleus is characteristically 
deep-staining, apparently homogeneous except for a few, barely 
visible, large nucleoli (fig. 52). The granules are at first small, 
but always larger than the eosinophilic granules, and stain very 
deeply blue (fig. 53). The granules become coarser, meanwhile 
maintaining their deep coloration. These same cells in the 
blood smears have a lighter-staining, centrally located nucleus, 
and their basophilic granules show a violet or lilac tinge (fig. 12). 
The nucleus of this cell in the marrow, due to its deep-staining 
and apparently homogeneous character, suggests degeneration. 
