30 MONOGRAPH OF THE FRESH WATER IIL. 
terrupted between the rays of the dorsal fins. The same is observed on the lower 
part of the tail from the anus to the caudal fin. On the abdomen and belly the 
layer is so thin that the flakes are exposed as soon as the skin is removed, 
§ 9. THE SKIN AND THE LATERAL LINE IN CorrTors. 
The skin in Cottoids is generally scaleless, and, in most cases, smooth. The 
Hemilepidoti of the marine tribe constitute the single exception, and even here 
they exist merely in bands or patches scattered over the body. The fresh-water 
species, however, are absolutely scaleless. 
In several Cotti, the skin on the thoracic region is beset with very minute 
asperities, perceptible only to the touch when the finger is passed from, behind 
forwards. 
On examining under the microscope the skin overlying the head of Cotti, we 
observe in its thickness small irregular star-like ossifications which are more 
developed in Acanthocotti so as to become sensible both to the touch and naked 
eye. In Triglopsis, the skin does not, even under the microscope, exhibit any- 
thing m its muscular texture; whilst in Cottopsis its whole surface is prickly from 
head to tail. There can be no doubt that those prickles are the same parts which 
we observe on the thoracic region of Cotti, only in Cottopsis they assume their 
maximum of development. Not having the opportunity of examining their struc- 
ture in Cottopsis, we cannot venture any opinion as to their signification; whether 
the homologues of true scales or a production of the skin peculiar to fishes 
unprotected with scales. 
The lateral line in Cottoids has a very remarkable structure, which could hardly 
have been suspected had the discovery of the genus Triglopsis not been made. Its 
beauty and development in the latter is such as to leave no doubt that it forms a 
regular, cartilaginous tube, with a series of quite large openings outwards (Plate IT, 
Fig. 11, 77) communicating through a corresponding series of pores of the skin, 
with the surrounding medium. ‘The removal of the skin exposes this tube, which 
still adheres to the sides by the layer of dermic muscles; after this layer is removed, 
the cartilaginous tube may be detached from the tail forwards, where it is seen to 
be united with the head. It passes through a channel of the occipital bones, sending 
down a branch along the preopercular, into the lower jaw. Proceeding forwards it 
branches off again in advance of the orbit, one branch running along the upper 
edge of that cavity into the nostrils, the other following its lower edge through the 
chain of suborbital bones into the nostrils also. 
That the lateral line in Triglopsis is intended to supply water to the system, 
there can be no doubt; and as little, that it answers the same end in other fishes. 
Its structure may be diversified according to the natural groups; this constitutes 
its morphology; but its philosophic meaning is the same throughout the whole 
range of the class. 
