90 BULLETIN OF THE 
present in large specimens as well as in small ones, in quantity almost, if 
not quite, as great in the one case as in the other; but that it becomes 
disguised in the former case, and in a manner that will appear presently. 
Figures 9 and 10, Plate II., are from sections of the integument 
and immediately underlying tissues of the dorsum of the head of two 
individuals, 19 mm. and 72 mm. long respectively. It will be noticed 
that the epidermis ‘does not differ essentially in thickness or structure. 
In Figure 9 it is about 0.028 mm., while in Figure 10 it is slightly 
thinner, though in reality it should be a little thicker, some shrinkage 
having taken place here. With the sub-epidermal connective tissue 
(con’t. tis.), however, the case is quite different. In Figure 9 its thick- 
ness is 0.056 mm., while in Figure 10 it is about 0.025 mm., over 
the pigment; and it will be seen that in both the pigment (pig.) is 
situated in the deepest stratum of the connective tissue, adjacent, or 
very nearly so, to the muscles (mx.). 
Within the sub-epidermal layer, in all the larger specimens, there is 
found a dense and intricate network of blood-vessels and capillaries. 
In general, the vessels of this network appear to run quite uniformly in 
one plane, situated about midway between the epidermis and the pig- 
ment layer. In many places, however, they will be seen, in sections, to 
approach very close to the epidermis, or at least to its basement mem- 
brane, which is at times quite distinct. These vessels are shown in 
Figure 10 (va. sng.) ; also in Figures 4 and 11 as surface views from 
nitric acid glycerine preparations. Their walls are so thin as to be 
scarcely distinguishable from the surrounding connective tissue. In- 
deed, in parts of many sections their presence can be detected only by 
the blood-corpuscles, which are very different in appearance from the 
connective-tissue cells, owing to their larger size, more elliptical outline, 
distincter nuclei, and slightly yellowish homogeneous non-stainable (in 
heematoxyline at least) cell protoplasm. The connective-tissue layer 
in which these vessels are situated is somewhat different from cither 
the layer above or that below it: its fibres are more closely compacted 
together, it contains more cellular elements, and it takes stain rather 
more readily than do the adjacent layers. I am inclined to believe 
that many of these cellular elements are leucocytes. I may here add 
that the blood-vessels shown in Figures 4 and 11 are none of them 
of capillary fineness, since in none of them are the blood corpuscles 
arranged in a single row, as is characteristic in capillaries. The cap- 
illaries are still smaller, and from the method of preparation and 
delineation are not shown here. 
