THE HISTOLOGY OF THE BLOOD OF LARVA OF ZEPIDOSIREN PARADOXA, 457 
naturally smaller nuclei, but are distinguished by the reaction of the nuclei. The 
protoplasm has an open reticulum, but is relatively small in amount. The outer layers 
_ are frequently seen to be fibrillar, the fibrillee bemg arranged circumferentially. There 
are also fine reddish granules in many of the cells, which, I take it, would correspond 
to GieLi0-Tos’s hemoglobigenic granules. 
3. The next class of cells is found only in the large sinuses. The nucleus is of the 
same dimensions as that of the cell just described ; it is round or oval, and selects only 
the eosin; the colorisation is reddish-yellow, the nucleoli are closely packed, and 
joined into a coarse reticulum by bars staining yellow like the rounded masses of the 
nucleoli. ‘The mitotic figures, which are very numerous, belonging to this class of cell, 
are distinouished by their yellow chromosomes. The protoplasm varies in amount ; it has 
an indefinite warm tint, and many of the cells have yellow granules. The peripheral 
layer is fibrillar, and round the nucleus the protoplasm shows a wide-meshed reticulum. 
Looking at these three varieties of cell, it is clear that the third is an erythroblast 
containing hemoglobin. It is almost equally clear that the second is a stage of the 
third—that, in fact, it is a primary erythroblast. The spleen, therefore, is a seat of 
origin of the erythroblasts, but do they arise by multiplication of erythroblasts which 
have entered the organ from without, or by new formation from the spleen cells? I 
conclude for the latter alternative, for the following reasons. 
While it is possible that the erythroblasts having nuclei characteristic of heemoglobin- 
containing corpuscles might be derived by division from the red blood corpuscles in 
the sinuses of the previous stage, it is not possible that cells with nuclei which do not 
show that reaction should be derived from heemoglobin-containing corpuscles. They 
might arise, however, by division from non-hemoglobin-containing erythroblasts 
derived from without, but their numbers are far out of proportion to the number of 
mitotic figures, so that one is driven to believe them to be a further phase of the larger 
cells of the first category. As a matter of fact, in cells with all the characters of these, 
here and there one occurs with a definite concentric fibrillar condition of the protoplasm 
(fig. 33, Pl. IV.), which I take to be the first stage in the conversion of the cell into an 
erythroblast. 
I think, again, that itis reasonable to derive these cells of the first category from the 
mesenchyme of the original rudiment. It is very hard to say at this stage whether 
their protoplasm is actually free, or part of the general protoplasmic framework ; and as 
this is the last stage of the series available, I am unable to say whether any part of the 
original cellular columns is retained in its primitive form, to give rise continuously to 
new budded-off elements; or whether the cells are all set free in the meshes of the 
reticulum, and give rise by continuous division to new elements. 
It seems justifiable to conclude that the original spleen cells, by a series of changes 
in the protoplasm and nucleus, become converted first into non-hemoglobin-containing 
erythroblasts, and that these, in turn, acquire hemoglobin and become the young red 
cells, and that the cells I have described represent the stages in the process. 
