516 MR. F. E. BEDDARD ON THE DEVELOPMENT AND [Dec. 7, 
by their smaller size, by their very deeply stained protoplasm, and 
by the fact that they nearly always contain a large number (3-5) of 
small nuclei close together. I have not yet succeeded in detecting 
these cells in the follicular layers, but I am nevertheless inclined to 
think that they are migratory leucocytes. I am at a loss, however, 
to account for the almost universal division of their nuclei into four 
or five. 
The presence of leucocytes in almost all the tissues and glands 
of the body is so well known that I need not give any detailed 
references ; the presence of these cells is not, however, to be con- 
founded with the migration of follicular cells. If, however, the 
identification of the follicular epithelium with a layer of immigrated 
leucocytes be right, there can be no distiuction between the two pro- 
cesses. The observations recorded in this paper, however, plainly 
show that in Protopterus at least there can be no possible confusion 
between follicular cells and lymphoid corpuscles, which is contra- 
dicted by so many other developmental facts. Unless it can be 
shown that lymphoid cells may arise from the direct metamorphosis 
of germinal epithelial cells it is quite absurd, in the present case at 
any rate, to allow any homology between follicular cells and im- 
migrated white lymph-corpuscles. 
Stege 111.—In this stage (figured diagrammatically in fig. 3, plate 
xxviii. of my former paper) the follicular epithelium is undivided 
from the ovum by any trace of membrane; the celis of which it is 
composed have dwindled down to a single layer ; their diameter bears 
a very small proportion to that of the enclosed mass of yolk, which 
has enormously increased in size. The cells of the follicular epithe- 
lium are still filled with yolk-spherules presenting no differences 
from the yolk-spherules which make up the substance of the con- 
tained mass. Their nuclei are conspicuous and round in shape. The 
follicular cells appear to continue to take a share in the nutrition of 
the body from the fact that they are large and well developed, and 
that the interstices of the protoplasmic network are largely filled with 
yolk-spherules: occasionally (e. y. figs. 7, 8, a) the nuclei of the folli- 
cular cells showed signs of degeneration ; this is probably preliminary 
to the evacuation of the cell-contents into the interior. Here and 
there the follicular cells appeared to be proliferating, the budded-off 
cells moving into the interior ; two such instances are shown in figs. 
7, 8. It is of course a difficult matter to decide how far the appear- 
ances shown in the two figures cited are due to the proliferation and 
migration inwards of the follicular cells; they might be explained, 
by reference to earlier stages, as central cells which have still re- 
mained in contact with the follicular layer, only that they occur on 
all sides, and it has already (p. 511) been stated that the central cells 
are only in contact with the peripheral for a limited area. On the 
other hand, a careful comparison of the example from which fig. & 
is taken with another in pretty much the same stage of development, 
only younger, as evinced by its smaller size, reveals the important 
fact that the larger contains, in any given section, a larger number of 
cells in its interior than the smaller. The larger was rather more 
