1886. ] STRUCTURE OF THE OVUM IN THE DIPNOI. 513 
These, like the last, are connected with the germinal epithelium, 
covering the outside of the ovary, by a pedicle of epithelial cells, 
which is nearly of the same width as the whole structure and its 
follicle. The germinal epithelium is in a condition of very active 
multiplication, the nuclei being very closely crowded together. 
The layers of cells which surround the central mass cannot be 
differentiated ; they present the appearance of a mass of cells con- 
tinuous with the germinal epithelium and forming a layer of cells 
three or four deep ; only here and there (fig. 10, 5/) were traces of the 
irruption of the stroma in the shape of small blood-capillaries. The 
cells which constitute this peripheral layer are precisely similar in 
their character to the cells which form the outermost of the peripheral 
layers in Stage I. 
In two instances belonging to this stage, which I have been able to 
study, the homogeneous darkly-staining mass produced by the 
solution and fusion (?) of the protoplasm of the central cells was 
much more in amount than in the last described stage. Fig. 11 
of Plate LIII. represents the central mass of cells, which are seen to 
be divided up into partly or entirely isolated clumps by the formation 
of this homogeneous mass, which contains also free nuclei (fig. 11, 2). 
In the third case the condition of the central cells, so far as this 
fused mass of protoplasmic material is concerned, was much the same 
as in Stage I. 
On the whole these facts appear to indicate that the bodies belong 
to a somewhat earlier stage than those just described and shown in 
fig. 1 of Plate LII. Their small size, the undifferentiated condition 
of the peripheral layers, as well as the very small amount of stroma 
(blood-vessels) between the cells of these layers, appear to me to 
point to this conclusion. On the other hand, the greater amount of 
change in the central cells, z. e. the inereased amount of the deeply- 
staining fluid substance between isolated clumps of cells, is against 
such a supposition, as it is evidently a further development of a 
process which has only just commenced in the developing structure 
which J have last described. This latter reason is perhaps not a very 
powerful argument, because it may easily be supposed that the pro- 
duction of the semifluid protoplasmic substance may be hastened or 
retarded ; the same may be said with regard to the specialization of 
the follicular layers, only that a specialization in the instances observe! 
by myself goes together with increase of size of the whole body. 
Accordingly I am inclined to believe that the bodies displayed in 
fig. 9 of Plate LIII. belong to a younger stage than those illustrated 
in fig. 1 of Plate LIL. 
Stage 11.—The different layers composing the foliicle are more 
differentiated, and each individual layer is now quite recognizable, 
Commencing from the outside, we have the secondary follicular layer, 
between which and the follicular layer proper is a well differentiated 
vascular layer, which is easily to be made out through the whole 
circumference ; the blood-vessels are filled with blood, and appear 
as round, elliptical, or elongated according to the angle of the 
section. The follicular layer has the appearance of being only 
Proc. Zoou. Soc.—1886, No. XXXIV. 34 
