452 H. E. JORDAN 
stricting pseudopods of such cells produce bodies comparable 
with the blood-platelets of megakaryocyte origin in mammalian 
marrows. 
DISCUSSION AND CONCLUSIONS 
This search for the amphibian homologue of the mammalian 
giant-cell from which the blood-platelets take origin has revealed 
two types of cells which in a measure fulfill requirements, namely, 
the polymorphonucleated neutrophilic leucocytes and the throm- 
bocytes. That the so-called megakaryocytes of red bone- 
marrow of mammals (e.g., of rabbit and guinea-pig) do actually 
at certain stages liberate blood-platelets can be abundantly 
demonstrated by the Wright” technic. These mammalian cells 
are commonly polymorphonucleated, occasionally polynucleated. 
Their faintly basophilic cytoplasm contains an abundance of fairly 
uniform metachromatic granules. These cells are not phagocytic, 
their occasional content of a leucocyte or two, generally eosinoph- 
ilic, is probably to be interpreted as an invasion following early 
stages of degeneration. Under certain conditions these cells are 
erythrocytopoietic. ‘The mammalian megakaryocyte also traces 
its origin to the common lymphocyte (hemoblast) ancestor of 
the blood-cells, both in the yolk-sac and in the red marrow. 
In both locations the nuclear characteristics are very similar, 
and the apparently identical granular cytoplasm produces com- 
parable blood-platelets in an identical manner (Jordan). More- 
over, in the yolk-sac the smaller, usually binucleated, type of 
these giant-cells may differentiate into erythrocytes (Jordan).” 
Wright?’ has suggested that the thrombocytes of Amblystoma 
represent the megakaryocytes of mammalian red marrow. But 
the thrombocyte resembles the megakaryocyte only in respect of 
its metachromatic granules scattered throughout a lightly baso- 
philic cytoplasm, and its elimination within the blood of gran- 
ulated globules similar to platelets, leaving eventually a naked 
nucleus. Within the bone-marrow it apparently does not lib- 
erate ‘platelets,’ in which respect it contrasts sharply with the 
mammalian giant-cells. Moreover, these cells differ greatly in 
regard to nuclear characteristics. The thrombocytes resemble 
