THE SCALES IN SOME TELEOSTEAN FISH. 45 
DEVELOPMENT. 
The first trace of the scales in Gadus callarias appears 
when the animal is between 3 and 4 cm. in length. The 
skin consists of an epidermis, which is very readily detached, 
and which, in the majority of preserved specimens, is 
altogether wanting. This is a fact of some importance 
which should be borne in mind, since the absence of this layer 
in much preserved material is doubtless the cause of the 
discrepancy in the accounts given by writers as to the part 
played by the epidermis in the formation of the scale. In a 
freshly caught fish it can be seen, as a soft, thin, almost 
gelatinous membrane, which tends to become separated 
when the animal is put into any other than its natural 
medium. A surface view of this membrane is shown in 
Fig. 1, taken from an animal 11cm. in length, Fig. 2 repre- 
senting a section through the same membrane in a somewhat 
older specimen. It consists of rounded or slightly fusiform 
cells, crowded together, each cell having a relatively large 
and well-marked nucleus. Opening on to the free surface 
are large numbers of spherical glands, the openings of which 
are proportionately small. Chromatophores are distributed 
throughout the thickness of the epidermis as well as on both 
its inner and outer aspects. 
On comparison with the epidermis of Lepidosteus, though 
there is a certain general resemblance, there are points of 
marked difference. In this animal, Nickerson (16) describes 
two kinds of glandular structures—one, the larger, oval in 
shape, with the long axis perpendicular to the surface of the 
body, and which are irregularly distributed ; the other, con- 
siderably smaller, more numerous and spherical, the majority 
of which occur “ near the surface, where many of them open.” 
Nickerson remarks that the latter “do not appear to have 
been recognised by previous observers.” He thinks that 
they are the true mucin secreting glands, the former having 
“the function of secreting some component of slime other 
than mucin,” 
