PISCES. 
the fish, as may easily be proved by drying it 
with a napkin, after which operation it soon be- 
comes again covered with mucus, which issues 
from the openings of these pores. 
In the Tunny ( Scomber thynnus ) there runs 
beneath the skin, following the entire length of 
the lateral line, an organ of a redder colour 
than the rest of the flesh, from which the little 
tubes forming the lateral line proceed, each 
tube receiving a nervous filament from the 
great lateral nerve. On raising the integument 
over this glandular organ a large vessel is seen, 
which, besides giving off arteries to the neigh- 
bouring muscles, furnishes an infinite number of 
branches to the glandular mass, beneath which, 
at nearly an inch from the surface, runs the lateral 
‘branch of the eighth pair of nerves, which in 
most other Fishes is situated immediately be- 
neath the skin. It is in the Raide or Skates, 
however, that this system of vessels is most 
largely developed. In these broad-bodied fishes 
there is found upon the ventral aspect of the 
body a large canal which surrounds the pro- 
minent muzzle, forming very regular angles and 
windings, distributes its secretion hy three or 
four branches on each side, and then winds 
upwards to terminate by different openings. 
There is, moreover, on each side at the external 
angle of the branchie a kind of sac which is 
round and of a whitish colour, which receives a 
large branch from the fifth pair of nerves, from 
which proceed a number of long simple vessels 
which run in radiating fasciculi in four or five 
different directions, and open at remote points 
on the surface of the body. 
In Sharks the entire substance of the snout 
is made up of a dense cellulosity filled with a 
mucilaginous fluid, in which are imbedded fas- 
ciculi of tubes that open upon the surface of the 
skin by wide orifices. Besides these there are 
large vessels of similar character, one of which 
runs along the whole length of the animal on 
each side. Innumerable muciparous follicles 
contribute likewise to lubricate the skin, more 
especially in the vicinity of the snout. 
By far the greater number of genera in the 
class before us are covered with imbricated 
seales, which overlap each other like the tiles 
of a house; the external and visible portion of 
these scales is covered with a thin layer of der- 
mis, which soon dries on exposure to the air; 
their internal or concealed part is lodged in a 
cavity which is a kind of sacculus hollowed out 
in the dermis itself, or formed by one of its 
replications—an arrangement which at first 
sight appears very different from what exists in 
Lizards and Serpents, in which what is called 
a scale is only a production of the cutis covered 
by the epidermis, that on the outer surface 
assumes a greater consistency and thickness ; 
but in the genus Scienus we have an inter- 
mediate arrangement between the imbricated 
scales of Fishes and what is met with in the 
scaly Reptilia. In the genus above mentioned 
the folds of the dermis are o¢cupied by a cal- 
careous plate, constituting a true scale easily 
separable from the cutis which envelopes it. 
We have only therefore to suppose the texture 
of this layer of cutis to be thinner and more 
973 
delicate, and we arrive at once at the scale of 
a fish, which seems in a fossa excavated in the 
cutis. In Fishes the scales thus implanted in 
the true skin were supposed by Cuvier to have 
no vascular connection with it, but to originate 
like a shell in the mantle of a mollusk by the 
gradual deposition of ‘consecutive layers depo- 
sited from the dermis; and all their varieties of 
surface, their different sculpture, the ridges or 
spines with which they are sometimes armed, 
and which frequently render them very beautiful 
objects for the microscope, were generally 
thought to have a similar origin. 
Dr. Mandl* appears to have been the first 
who, by a microscopic examination of the inti- 
mate structure of the tissues which enter into 
the composition of the scales of Fishes, arrived 
at just conclusions relative to the mode of their 
formation, and proved that, so far from being 
mere exudations of corneous matter, they are 
produced, like the teeth and osseous tissue, by 
a true internal growth and nutrition. 
The following is an abstract of the result of 
Dr.Mand1’s researches upon this interesting sub- 
ject, in which he satisfactorily proves that the 
scales of Fishes consist of two layers, of which 
the inferior exhibits a structure analogous to 
that of fibro-cartilage, whilst the superior re- 
sembles corpuscular cartilage, and is evidently 
formed by the developement of primitive cells. 
Taking a well-developed scale, as that of a 
Carp, for an example, it is easy to perceive that 
its surface is marked with longitudinal lines 
arising from a common centre, and running to- 
wards the periphery of the scale, the number 
of which it is generally very easy to determine. 
The place towards which these lines converge 
is ‘a space of variable dimensions, called by 
Dr. Mandl the focus. Between the longitudinal 
lines are seen, running parallel to the circum- 
ference of the scale, a very considerable number 
of concentric lines, which are crossed by the 
longitudinal ones at right angles; these are 
named “ cellular lines,” because they owe their 
origin to the developement of cells. Besides 
the parts above mentioned, many kinds of 
scales exhibit upon their surface, and upon 
one of their edges, spines of different forms, 
called by Dr. Mandl the deeth of the scale, a 
name which he founds upon the mode of de- 
velopement of these appendages. Around the 
longitudinal and transverse lines, more espe- 
cially near the point where the former converge 
towards the “ focus,’ are numerous yellowish 
corpuscles of an elliptical shape, named the cor- 
puscles of the scale. 
Lastly, if the upper layer of the scale be 
raised or torn, an inferior stratum is displayed, 
of a fibrous character. These different struc- 
tures he then proceeds to describe seriatim. 
1. The longitudinal lines, which, arising 
from the focus of the scale, run towards its 
periphery, play an important part in the ana- 
tomy of the tissue we are examining, and when 
highly magnified are found to be so many ca- 
nals exhibiting in the scales of different species 
* Recherches sur la Structure interne des Ecailles 
des Poissons. Par le Dr. L. Mandl. Ann, des 
Sc. Nat. tom. xi. 
