472 H. E. JORDAN 
part as lymphoblasts. The extravascular hemoblasts develop 
into lymphocytes and granulocytes, which may enter the vas- 
cular spaces secondarily. The lymphocytes of the circulating 
blood are apparently only slightly modified marrow lympho- 
blasts or hemoblasts, which occur both intra- and extravas- 
cularly. A certain number of neutrophilic leucocytes also 
originate intravascularly. Circulatory lymphocytes also may 
differentiate further into neutrophilic leucocytes. 
6. Pseudopod constriction and cytoplasmic fragmentation of 
leucocytes are two fundamentally distinct processes leading to 
similar results, namely, the production of free cytoplasmic 
globules. Pseudopod formation and constriction is a common 
property of leucocytes; fragmentation is a degeneration phe- 
nomenon associated with nuclear pycnosis and subsequent dis- 
integration. Lymphocytes and eosinophilic leucocytes produce 
the hyaline bodies; neutrophilic granulocytes, thrombocytes, 
and certain lymphocytes with metachromatic granules produce 
platelet-like bodies. Globules with basophilic granules arise 
from pseudopods of mast-cells. Platelet formation from mega- 
karyocytes in mammalian red bone-marrow is apparently a by- 
product of this common property of leucocytes and their deriva- 
tives, and especially of the disintegration of senile types of these 
cells. 
7. The amphibian homologue of the mammalian hemogenic 
giant-cell is a large mononucleated cell with a relatively large 
nucleus, comparable to the similar mononucleated giant-cell of 
mammalian marrow from which develop the polymorphonu- 
cleated (‘megakaryocyte’ with ‘basket nucleus’) and multinu- 
cleated older types. Both cells differentiate from a hyper- 
trophied primitive lymphocyte or hemoblast. 
8. The polymorphonucleated neutrophilic leucocytes contain 
a conspicuous centrosphere which may include a simple, a bi- 
lobed, a double, or a multiple centrosome. These cells do not 
divide mitotically. It is suggested that mitotic incapacity on 
the part of these cells is the result of a relative nutritive want in 
consequence of the high degree of specialization involved in the 
elaboration of the metachromatic granules. The underlying 
