440 . DR THOMAS H. BRYCE ON 
This is due in some measure to different methods of treatment, the earlier stages being 
celloidin sections stained with safranin, while these are paraffin preparations stained with 
iron hematoxylin. 
Two kinds of corpuscles are to be recognised. The first, evidently the direct 
derivatives of the corpuscles of the previous stage, have a large round or slightly oval 
body, measuring 50 « to 60 , and a round nucleus which has the same general features 
as described for that of the earlier elements. 
The protoplasm round the periphery of the cells has undergone a transformation 
into a broad band of delicate concentric fibrils. Within this the protoplasm has a 
delicate alveolar structure and contains large yolk grains, and im some corpuscles clear 
vacuoles. In the particular cell drawn (fig. 3, Pl. I.) there was a homogeneous area at 
one pole of the nucleus which I take to represent the centrosomal area of the earlier 
corpuscles, but there is no distinct centrosome, nor is there a radial sphere. Most of 
these cells are round, but a few are oval in shape (fig. 4, Pl. I.).* The cell of this 
class drawn has only a few yolk grains, the alveolar disposition of the protoplasm is 
distinct, and at each end of the elongated body there is a group of minute darker- 
staining granules, which I interpret as the cross sections of the peripheral fibrillze of 
the other cells, and which, as will appear later, in more advanced corpuscles come to 
occupy this situation in profile sections. 
The second kind of corpuscles are smaller cells, about 39 « in diameter (figs. 5 and 
6, Pl. I). The nucleus is notched or lobed, but has otherwise the same general 
characters as that of the larger corpuscles. The protoplasm is either uniformly alveolar 
or vacuolated. There is a distinct sphere and centrosome, and the peripheral band is 
absent. 
The vacuolation of the corpuscles at this and later stages is evidently connected 
with the using up of the yolk. It is seen in the general tissue cells also. The fibrillar 
hand is seen only in the blood corpuscles, and is clearly the first stage in the con- 
version of the primitive blood corpuscles into the passive hemoglobin carriers of later 
phases. 
It seems to be a fibrillar transformation of the peripheral layers of the protoplasm, 
and not a mere disposition of an alveolar meshwork; and as none of the corpuscles 
have yet the biconvex disc shape, it is not the mere consequence of the shape of the 
cell. 
While the mass of the corpuscles are thus assuming a passive role, certain remain 
as free mobile elements, constituting the second type of cell described, with its 
sphere and centrosome, and the lobing of its nucleus somehow associated with the 
activities of the cell. 
While one cannot at this stage, when there are yet no hemoglobin-bearing cells, 
call these elements leucocytes, it is to be noticed that in general morphological 
* Jt is probable that these are profile sections of the circular disc-shaped forms. 
