BLOOD AND BONE-MARROW OF FROG 457 
‘special leucocytes’ with minute or ellipsoidal eosinophilic granules 
characteristic of those forms which lack neutrophils, namely, 
certain mammals (e.g., rabbit, guinea-pig) and sauropsids, respec- 
tively, is a question of a different order, and one that need not 
here be further discussed. 
Having thus disposed of both these alleged amphibian homo- 
logues of the mammalian megakaryocytes, we may analyze the 
possibilities of still another type of cell. This cell occurs only 
sparsely. It contains a relatively enormous nucleus, with one or 
several plasmosomes, numerous irregular karyosomes, and a 
delicately reticulated vesicular nucleoplasm (fig. 73). The 
nucleus is enveloped with a variable shell of lightly basophilic 
cytoplasm containing metachromatic, lilac-colored granules. It 
may be assumed that this cell forms pseudopods which may con- 
strict and become free corpuscles. This amphibian giant-cell 
develops from a primitive lymphocyte and represents a hyper- 
trophied hemoblast. In all these respects, then, it corresponds 
with the mononucleated giant-cells of the red marrow of the 
femur of the rabbit. It has been shown that the polymorpho- 
nucleated giant-cells, the so-called megakaryocytes, develop 
from mononucleated giant-cells through nuclear modifications 
(Jordan). It seems that in the frog the marrow giant-cells 
develop only to the mononucleated stage. Possibly at certain 
periods this marrow also would show later polymorphonucleated 
phases. The usual statement that giant-cells are not found in 
the red marrow of forms below the mammals must therefore be 
revised. Careful study of the marrow of sauropsida may pos- 
sibly also reveal giant-cell homologues of even closer corre- 
spondence. 
Another important body of evidence supplied by this material 
concerns the monophyletic theory of blood-cell origin. Maxi- 
mow? has published a brief preliminary report on hemopoiesis 
in Rana temporaria, and interprets his evidence in accord with 
this theory. His material includes larvae and the adult bone- 
marrow. As regards the process in the latter, his statements 
are especially brief. However, the chief points are touched. 
My results agree completely with his earlier findings except in 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 25, NO. 4 
