444 H. E. JORDAN 
these pseudopods appear to constrict off spheroidal . granular 
fragments, resembling blood-platelets of mammals (figs. 30 and 
31.) The extreme viscosity of the thrombocyte cytoplasm 
would seem to account fully for the fact that these cells generally 
occur in larger and smaller closely adherent groups. One line 
of evidence casts doubt upon the interpretation of the projec- 
tions of the thrombocytes as pseudopods and the isolated bodies 
as segmentation products: The cytoplasm is unmistakably very 
delicate and very viscid; in contrast with all of the leucocytes of 
the marrow, the spindle cells of the marrow do not show pseudo- 
pods. This would seem to indicate that the ‘pseudopods’ of the 
thrombocytes are artifacts, formed through the operation of 
mechanical factors in the process of making the smears. On the 
other hand, numerous naked and disintegrating nuclei of throm- 
bocytes occur in the blood (fig. 32); these recall the naked nuclei 
of the megakaryocytes of mammalian marrows, and in a meas- 
ure support Wright’s suggestion that the megakaryocytes of 
mammals and the spindle cells of amphibia are homologous 
elements. 
The resemblance between the granular cytoplasm of the mega- 
karyocytes of mammals and that of the thrombocytes of am- 
phibia is very close; but it appears no more close than between 
this cytoplasm and that of the neutrophilic leucocytes. More- 
over, the constriction products of the pseudopods of thrombo- 
cytes, neutrophilic leucocytes and certain lymphocytes of the 
frog, and those of the pseudopods of the megakaryocytes of 
rabbit and guinea-pig are very similar. These corpuscles consist 
in common of a spheroidal viscid mass of faintly basophilic 
cytoplasm containing a central group of fine metachromatic 
spherical granules. The question of homology will be further 
discussed below. 
At this place must be noted the character of the nucleus. In 
the smear preparations this appears dense and chromatic (deep 
lilac) with numerous irregular vacuoles. In the marrow this 
nucleus is more oval, it contains a chromatic reticulum with 
numerous karyosomes, it stains much less deeply and it takes a 
blue color (figs. 42 and 43). Moreover, it shows several deep, 
