974 
every degree of formation from a simple furrow 
to a perfectly enclosed tube. 
The broad scales or plates which form the 
armour of the Syngnathide are traversed b 
similar canals enclosed on all sides, which, al- 
though separate at the margins, anastomose 
freely towards the middle of the scale. 
The longitudinal lines in all their forms con- 
stitute a series of hollow tubes that must be 
regarded as true canals. These canals traverse 
the scale in a longitudinal direction converging 
towards a focus, which, as will be shown here- 
after, is a centre of nutrition, so that most pro- 
bably these tubes perform the functions of 
nutritive vessels. 
2. The cellular lines, supposed by preceding 
writers to be merely lines of growth analo- 
gous to those observable upon the exterior 
of a bivalve shell, attentive examination shews 
to owe their arrangement to a very different 
cause, Originating in the developement of pri- 
mitive cells, which are ienicnat in the super- 
ficial stratum of the scale and gradually assume 
an elongated form, become filled with corneous 
matter, and ultimately arrange themselves in 
concentric lines of greater or less breadth, 
which only indicate by their uneven edges 
their original nature. 
3. The corpuscles seen in scales are precise] 
similar in their appearance to those met'wi 
in bone and cartilage, and are obviously of the 
same nature, They are distributed in the basis 
membrane, which seems to be an amorphous 
tissue resembling that in which the corpuscles 
of bone are deposited, and which forms the 
superficial stratum of the scale. 
4. The fibrous layer—On scraping off with 
a penknife the external surface of the scale, the 
cellular lines and the corpuscles with their 
basal membrane are removed, and the deep- 
seated stratum of the scale becomes visible, 
which is then seen to consist of fibrous lamelle 
composed of fibres that cross each other at 
regular angles, giving to this tissue the appear- 
ance of fibro-cartilage. This layer is thickest 
near the focus of the scale, and become gradu- 
ally thinner towards the edges.. 
5. The focus is the space towards which the 
longitudinal lines converge, but is not always 
situated in the centre of the scale; it is occu- 
pied by very large pale a Hear and by 
interrupted circular lines; such at least is its 
appearance in the scales of Acanthopterygenous 
ishes, but in the Malacopterygii, and more 
especially in those species which have mem- 
branous scales, it presents nothing but a smooth 
circumscribed surface without corpuscles or in- 
terrupted lamine, and is then generally sur- 
rounded by the concentric cellular lines. 
6. The teeth of the scales—The growth of 
the spines and other appendages seen upon the 
outer surface and posterior margin of many 
forms of scales, more especially in those named 
ctenoid by Agassiz, is a subject of very consi- 
derable interest, and to the old physiologists, 
who believed all scales formed by mere exuda- 
tion, must have been quite unintelligible. The 
production of these spines is in fact, according 
to the researches of Dr. Mandl, in every respect 
PISCES. 
similar to the growth of teeth, each bei 
enclosed in a distinct capsule and pedro 
in the following manner, as exemplified by 
the growth of a scale of Corvina nigra, one of 
the Scienide. 
The posterior margin of one of these ss is 
occupied by conical appendages, represented in 
a highly magnified condition in fig. 508. Each 
: of the oblong processes 
ae tee. here depicted is seen to be 
encl in an env 
from which, however, it is 
entirely separate, as is 
be 4 ~ fact that w ae 
e capsule is ruptured 
auld spine can be re- 
moved from it with the ut- 
most facility. Examined in 
detail, every one of these 
spines exhibits an 
zation and mode of growth — 
precisely similar to that of 
a tooth, being formed in its 
capsule exactly in a similar 
manner. The germ begins 
gradually to develope itself; 
it acquires roots, and be- 
comes distinctly composed 
of different layers, = that 
these spines may_wi ) 
priety be called the teeth of . 
the scales, in allusion to 
the mode of their develop 
i bat ment. The marginal 
A small portion of the are most connate 
Ci 
After Mandl. ) formed, and the whole sur 
face of the tooth smooth and continuous. In the 
two next teeth below, the developement is 
less advanced ; the extremities are truncated, the 
external layer of the tooth does not entirely cover 
it, but the roots are visible. Still lower down 
the teeth of the scale become more and mo 
imperfect, until the lowest are scarcely at al 
developed, and are barely distinguishable amon 
the surrounding corpuscles. 
In other families with denticulated 
the growth of these appendages is prec 
sinoiler, as in the Gobinides, Percoides, F 
ronectide, &c. 
From the above observations it becomes evi- 
dent that the scales of Fishes can no longer b 
ed as mere productions of secretion fro 
the skin, but must be considered as pe 
an inherent power of nutrition and a tf 
growth. The denticles which exist upon ma 
of these scales offer by their successive dev 
lopement a striking proof of this importa 
fact; while the canals whereby they are t 
versed, and the corpuscles belonging to thet 
structure, plainly intimate that their mode of 
developement is similar to what exists in the 
teeth and in the osseous system. eg 
The chemical composition of the scales 
Fishes, moreover, very nearly approx 
of 
