118 BULLETIN OF THE 
former is much the better; the latter is especially useful in the 
study of the glands of the epidermis and in bringing cell membranes 
into prominence. 
The young Lepidosteus in which I found the earliest indication of 
the formation of scales was about 145 mm. long and a little over 
eighteen months old. Klaatsch has stated that the scales appear upon 
the dorsal side of the body earlier than upon the ventral, and as the 
material studied was taken in this specimen (as in most cases) from 
near the ventral line, it is probable that the scales begin to form upon 
the dorsal portion of the body at a somewhat earlier age. 
Before the beginning of the formation of the scales the integument is 
about 225 thick. The epidermis is nearly twice as thick as the 
dermis and is made up of numerous layers of spheroidal or cuboidal 
cells (Fig. 1). The cells of the deepest layer are somewhat elongated 
in a direction perpendicular to the surface, and consequently have the 
appearance of indistinctly columnar epithelium. 
There are two kinds of glandular structures present in the epidermis. 
Those of one kind have a spherical, or more often ovoid or oblong form, 
with the greater axis perpendicular to the surface of the body, and 
appear in sections as spaces of corresponding shape. The long diameter 
in the larger of these spaces is not infrequently (Fig. 1) from one half 
to two thirds the thickness of the epidermis (75-100 pg). 
The glands are quite irregularly distributed, some areas being only 
very meagrely provided with them, while in others they are so crowded 
as to leave little more than thin filmy partitions between them. 
Sections parallel to the surface in such areas present a net-like appear- 
ance, the empty gland cells corresponding to the meshes. To each 
space there belongs a flattened nucleus, which is closely applied to the 
wall near its deep end. The whole structure is doubtless to be con- 
sidered as a single cell which has taken on a secretive function, — a 
unicellular gland. 
These glandular spaces sometimes appear empty, but are more often 
found partly filled by an indistinctly granular colorless substance 
(coagulum), probably precipitated by reagents from the fluid or semi- 
fluid secretion which they held during life (Plate I. Fig. 1, Plate II. 
Fig. 16). I do not find that these spaces have any means of communi- 
cation with one another, and only very rarely do I find one having an 
opening to the exterior. Klaatsch has described these as mucous 
glands. I have no doubt that they are concerned in the production of 
