184 PISCES. 



situated in the centre of the scale ; the circular are frequently in- 

 tersected by longitudinal lines, and of this arrangement there are 

 abundant examples. To determine the more minute structure of 

 the scales of Fishes is a subject attended with much difficulty. The 

 scales are always included within the cutis itself, and consequently, 

 unless the latter is injured, it is impossible for the scales to come 

 off. The layers, which cover the scales, are as follows: 1st. An 

 epidermis, formed of tessellated cells ; these may be found detached 

 in small masses in the slime that covers a Fish, and constitute its 

 principal part. 2d. A layer of pigment-cells; these are frequently 

 ramified, and are continued into spirally-contorted terminal canals, 

 which do not, however, anastomose with each other. 3d. The cutis, 

 consisting of a fibrous tissue, within the areolae of which is a deposite 

 of fat. 4th. A very fine layer of membrane, distinct from the cutis, 

 and in which linear-shaped depressions and elevations may be re- 

 marked corresponding to the concentric grooves and ribs of the 

 scales. This layer consists of fibres, which, in a histological point 

 of view, are related to cellular tissue. 



Each scale is lodged in a sac, formed by two lamellae of the cutis, 

 the superior of which is alone covered by pigment-cells and epider- 

 mis. Each scale has an inferior soft portion, consisting of fibro- 

 cartilage. It is not easy to determine whether or not the concentric 

 striae are merely the optical expression of the lamellae of the scale 

 lying upon each other. This part of the scale appears actually to 

 consist of bony tissue, although true osseous corpuscules are gener- 

 ally absent. The scales are, moreover, traversed by broader chan- 

 nel-like longitudinal lines ; these are, however, frequently absent, and 

 their nature and signification are unknown. 



The manner in which the scales clothe the body of Fishes varies 

 very much in the several genera, as do the feathers upon Birds. As 

 a rule, the scales lie in an imbricated fashion upon each other, leav- 

 ing a part of their border free, so that they abut against each other in 

 a variety of ways. Occasionally the upper edge of a scale is provi- 

 ded with a hook-shaped process, which catches in a depression of 

 the inferior edge of the next scale that covers it. The lines of di- 

 rection.of the rows of scales upon the body vary also. 



The form and contour of the scales present an almost endless 

 variety ; they are either round or oval, angular or provided with 

 undulated edges and projecting lobes ; these edges are fre'quently 

 dentated, and provided with several rows of spines. A row of pecu 

 Uarly-formed scales is situated upon what is called the lateral line, 



