BLOOD AND BONE-MARROW OF FROG 453 
platelets in respect of a very adhesive protoplasm, in consequence 
of which they frequently become grouped into larger and smaller 
masses. But this property of adhesiveness is characteristic also 
especially of the lymphocytes, certain of which also have a 
variable amount of metachromatic granules. 
The polymorphonucleated neutrophilic leucocytes of the frog 
seem at first to bear a much closer resemblance to mammalian 
megakaryocytes. They are of course smaller than the mega- 
karyocytes. While not of the extreme ‘basket’ form, the nu- 
cleus is frequently extensively lobulated. The centrosome is 
always conspicuous and frequently multiple, as described by 
Heidenhain for megakaryocytes. These cells contain, moreover, 
a very similar metachromatic granulation, which is likewise 
scattered through a basophilic substratum, the latter forming 
an exoplasmic layer of variable width. The granules of the 
amphibian neutrophilic leucocytes stain less deeply than those of 
the mammalian megakaryocytes, but otherwise they are very 
similar. Moreover, these leucocytes protrude pseudopods, which 
fragment to form platelet-like bodies, like those of megakaryo- 
cytes (figs. 61 to 68). These pseudopods even project into 
blood-vessels, as do those of the megakaryocytes (fig. 63). The 
presence of these alleged giant-cell homologues in the amphibian 
blood, as compared with the restriction of the megakaryocytes 
of mammals to the bone-marrow, might be due simply to the 
fact of the great size of the latter prohibiting entrance into the 
capillary circulation. It would seem on the basis of the histo- 
logic evidence that the neutrophilic leucocyte of amphibia meets 
more nearly the requirements of a megakaryocyte homologue 
than does the thrombocyte. 
However, the fact that no naked nuclei of these neutrophilic 
leucocytes occur, while such are numerous of thrombocyte origin, 
contravenes in a measure the assumption of homology between 
the polymorphonuclear neutrophilic leucocytes of the frog and 
the megakaryocytes of the marrow of the rabbit. In addition to 
this objection, there is the further contradiction that certain 
mammals have a red marrow containing both typical megakary- 
ocytes and typical polymorphonuclear neutrophilic leucocytes 
(e.g., cat, dog). 
