18 THE rERlODIC GROWTH OF SCALES IN GADID.E 



When scales are provided with spines, as in Ctenoids, the points of tliese may 

 be seen piercing the epidermis, and so appearing freely at the surface. The 

 derrree with which scales adhere to the skin is snl)ject to great variation in 

 dilFerent fish. In the herring, for instance, scales are very easily detached ; 

 but in Dactijlopterus volitans, etc., they are only separated from the skin with 

 much difticulty. Scales are never entirely free in the dermic pouch, as they 

 are always connected with its walls by fibrils of connected tissue, usually of 

 extreme fineness. In imbricated scales the free jjortion has a more or less 

 intimate connection with the skin, and so in extracting scales from the body 

 of the fish, the free portion carries with it debris of the skin, from which it 

 is frequently difiicult to separate it. In certain varieties of carp (mirror carp, 

 leather carp), in which, as one knows, scales may disappear on more or less 

 extended parts of the body, the scales show very varied connections with the 

 skin. On certain parts one meets with very large scales much imbricated, on 

 other parts the scales are still larger, but scarcely covered over, or even 

 entirely isolated. Extremely small scales are also found, which are completely 

 enclosed in the depths of the skin. The imbrication of scales ought to be 

 considered so far as a phenomenon of mechanical arrangement intimately con- 

 nected with the greater or lesser development of scales and with the degree of 

 their separation. 



2. The form of scales and their mode of orient at ion. The form of scales is 

 extremely variable. These variations occur not only in different species, but 

 in different regions of the body of the same fish. In each fish the large 

 scales covering the median region of the flank may be considered typical, that 

 is to say, they possess in the largest measure and with most constancy all the 

 proper characters of the species. Scales from the dorsal and ventral surface, 

 from the head and fins, frequently show more or less marked deformations, and 

 seem to lose some of their characteristic features. Scales oval at one place 

 may change into a circular form at another place, polygonal scales to circular 

 ones, elliptical to a more or less irregular form. 



Lobes at the margins of scales, spines, concentric ridges, and grooves may 

 vary considerably in number, and even disappear altogether in different parts 

 of the body. " Nothing is more variable than the external characters of scales, 

 and as in a tree one does not find two leaves exactly identical, so is it in 

 regard to the scales of fishes ; but the particular features of scales, as of leaves, 

 do not all vary at the same time, and thus there generally remain several 

 general characters of resemblance which scarcely allow us to confound the 

 scales of one species with those of another." The simultaneous presence of 

 cycloid and ctenoid scales was pointed out by Baudelot in the following : — 

 TrigJa lineata, Sargus Ilondeletti, Perca Jluviatilis, Pleuronedes solea, 

 Pleuronedes flesus, etc. 



The form of scales appears somewhat to depend upon their connection with 

 one another, their juxtaposition; thus scales isolated in the skin tend to have 

 a rounded or circular form (Lota, Anguilla, Ophidium). On the contrary, where 

 scales are large and much pressed the one against the other, they most fre- 

 quently take a polygonal form. The orientation of the long axes of scales in 

 relation to the axis of the body is usually fairly constant in those fish in which 

 there is a regiilar and distinct imbrication of scales. In fishes in which the 



