MUSEUM OF COMPARATIVE ZOOLOGY, 57 
must have been exceptionally frail, since separations of this kind are 
rare in adjacent regions. 
The thin layer of tissue next to the lens — in fact closely applied 
to it in many cases (Figs. 5 and 17, crn.) — is part of a layer that en- 
velops the entire eye, in many places lying close upon the pigmented 
layer of the retina. The portion in the region of the retina is undoubt- 
edly the sclera, and will hereafter be designated as such. The portion 
in the region of the lens may be regarded as representing all there is of 
a cornea excepting its epithelial layer ; but on this subject I shall speak 
further presently. The strands of connective tissue that have been 
spoken of as intervening between the epidermis and the eye in the 
smaller specimens are distinctly fibrous, and contain numerous small, 
much flattened connective-tissue nuclei. These strands are directly 
continuous with the sub-epidermal connective tissue of the surrounding 
regions, and are not largely continuous with the sclera, though in part 
they are (Fig. 17 a). 
In addition to the small flattened connective-tissue elements in these 
bands of connective tissue, a few much larger cells are found (el. con't.). 
They have distinct round nuclei, and each nucleus has a nuclear mem- 
brane and a nucleolus, The membraneless cell body is drawn out into 
one or more processes, usually two or three, which become lost among and 
are apparently continuous with the fibres of the connective-tissue strands 
in which the cells are situated, They are probably embryonal connect- 
ivo-tissue cells concerned in the production of the thick layer of this 
tissue that intervenes between the eye and the epidermis in older speci- 
mens (Plate IT. Fig. 6). In this older specimen (Fig. 6) a large num- 
ber of nuclei aro seen, in part immediately over the eye, and consequently 
in the same position as the cells regarded as embryonal connective-tissue 
cells in the young specimens ; but they are mostly at one side of the 
eye (Fig. 6, con't. tis.), and although some of them are undoubtedly 
cells of connective-tissue character, at the same time many of them are 
certainly not of this nature, but are probably leucocytes. As shown in 
Figure 6, there is over the eye in the large specimens a well defined 
dermal layer, drm., which usually remains adherent to the epidermis 
when the latter is removed. This layer is nearly structureless, though 
fine fibres are not uncommon in it. In the specimen shown in Figure 6, 
the entire thickness of the tissues over the eye is about 392 a, of which 
103 a is epidermis and 289 p sub-epidermis. About midway between 
the epidermis and the eye there is a thin stratum of formed connective 
tissue (st. con't,), much denser than the surrounding tissue ; and imme- 
