470 H. E. JORDAN 
in adipose cells of insects ‘‘may be for the purpose of securing an 
increase of the nuclear surface to meet the physiological neces- 
sity due to the active metabolic interchange between the nucleus 
and cytoplasm” (p. 509). Even in cases where the original 
centrosome has fragmented, presumably under the influence of 
cytoplasmic specialization, the effective factor in determining 
amitotie division may still in part be the metabolic condition 
following a certain degree of nucleo-cytoplasmic balance. That 
the fragmentation of itself is not in all cases effective seems 
proved by the case of the mitotically dividing blastomeres of 
the Cummingia embryo in which pluricorpuscular centrosomes 
abound. In the ciliated cells of vertebrates a partitioned cen- 
trosome, under the metabolic conditions underlying the type of 
differentiation characteristic of a cell developing cilia, is gen- 
erally incapable of supporting mitotic division; in the more 
vigorous blastomeric cells of Cummingia, characterized by pre- 
sumably different metabolic conditions, such a centrosome may 
still be able to function in indirect division. 
Probably the most important result of this search for the am- 
phibian homologue of the mammalian giant-cell turns out to be 
the light shed upon the significance of the hemogenie giant-cells, 
especially the so-called megakaryocytes of mammals, and upon 
the morphologit and genetic significance of the blood-platelets. 
Though both thrombocytes and polymorphonucleated neutro- 
philic leucocytes show certain characteristics in common with 
the mammalian megakaryocytes, the genuine amphibian homo- 
logue is a very large mononucleated cell, comparable with a 
similar giant-cell of mammalian marrow from which the poly- 
morphonucleated megakaryocytes develop. These cells are the 
homologues also of the mono- and polymorpho- and polynucle- 
ated hemogenic giant-cells of the mammalian yolk-sac during its 
hemopoietic phase.!2 These cells in all of these locations develop 
from the primitive lymphocyte or hemoblast. This study of 
frog’s marrow has shown that pseudopod formation and constric- 
tion is a characteristic common to leucocytes at all stages of their 
history. Moreover, it is well recognized that cytoplasmic frag- 
mentation is a concomitant of degeneration. The processes by 
