SCALES. 



[ 677 ] 



SCALES. 



spine-like processes (figs. 6 b & 9), with 

 rounded or angular bodies, resembling the 

 last in appearance, arranged in rows at their 

 bases (fig. 8). 



The scales of the eel appear to be princi- 

 pally composed of similar bodies, differing 

 only in form, and arranged in concentric 

 rows (PI. 22. figs. 20 & 20 a). They are 

 solid, impregnated throughout with calca- 

 reous matter, which is left after incinerating 

 the scales, retaining the original form of the 

 bodies (tig. 21). 



In the scales of some fishes, particularly 

 those of extinct genera and species, lacunae 

 and canaliculi resembling those of bone 

 (PL 22. fig. 1 c), with Haversian canals, are 

 met with. A vitreous or enamel-like layer, 

 having the structure of dentine, is also met 

 with in the form of an external coating. 



The structure of the spines or spine-like 

 scales of the skate is curious. The larger of 

 them consist of a button-like base, sur- 

 mounted by a sharp process (PL 22. fig. 3). 

 The outer and lower part of the base is 

 opaque-white, and consists of an imperfectly 

 fibrous tissue with large areolae (tig. -37). 

 The spine is hollow, the cavity being con- 

 tinuous with that of a rounded body, partly 

 immersed in the white substance (PL 22. 

 fig. 3 a). The cavity is filled with a pulp, 

 consisting of lax areolar tissue with minute 

 cells; whilst its walls are composed of a 

 hard substance traversed by branched canals 

 resembling those of dentine (fig. 4). The 

 substance of the smaller spines (fig. 2) 

 exhibits the same dentinous structure 

 (fig. 5). 



PL 22. fig. 10 represents one of a longi- 

 tudinal row of scales extending along the 

 middle of the side of the body of most 

 fishes, and traversed by a tube (a), formerly 

 supposed to give exit to the mucous secre- 

 tion of the surface, which view has lately 

 been thrown into doubt. The tubes are 

 visible to the naked eye, and produce the 

 lateral line, as it is called. 



The scales of fishes contain a large amount 

 of inorganic matter, composed principally of 

 phosphate of lime, but mixed with the car- 

 bonate. The organic basis consists of a 

 cartilaginous substance. 



Some years since, Agassiz founded a 

 classification of fishes upon the structure of 

 the scales, having found that with differences 

 in the scales other great and important di- 

 stinctions were in harmony. The system 

 has been found of eminent service to the 

 geologist ; although later researches have 



shown that scales presenting the charac- 

 teristics of those belonging to fishes of dif- 

 ferent orders in this system have been 

 found upon the same fish. 



The arrangement was as follows : 



Scales enamelled. 



Ord. 1. Ganoid fishes. Those the skin 

 of which is regularly covered with angular 

 thick scales, composed internally of bone, 

 and externally of enamel. Most of the 

 species are fossil, the sturgeon and bony 

 pike being recent. 



Ord. 2. Placoid fishes. Skin covered irre- 

 gularly with large or small plates or points 

 of enamel. Includes all the cartilaginous 

 fishes of Cuvier, except the sturgeon ; as 

 examples may be mentioned the sharks and 

 rays. Many are fossil. 



Scales not enamelled. 



Ord. 3. Ctenoid fishes. Scales horny or 

 bony, serrated or spinous at the posterior 

 margin. Contains the perch and many other 

 existing species, but few fossil. 



Ord. 4. Cycloid fishes. Scales smooth, 

 horny or bony, entire at the posterior mar- 

 gin ; as the salmon, herring, roach, and 

 most of our edible and freshwater fishes. 



Most of the fossil fishes belong to the 

 first two orders, and most of the recent to 

 the third and fourth. 



BIBL. Agassiz, Ann. Sc. Nat. 2. xiv. ; 

 Mandl, Ann. Sc. Nat. 2. xi., xii., xiii. & xiv. ; 

 Reade, Ann. N. H. 1838, ii. 191 ; Miiller, 

 Wiegm. Archiv, 1843, 298; Vogt, Zoolog. 

 Briefe, ii. ; Williamson, Phil. Tr. 1849,435, 

 & 1851 ; Salbey, Struct, and Growth of 

 Scales of Fish, Ann. N. H. 1870, v. 67. 



SCALES OF INSECTS. The fine dust 

 which adheres so readily to the fingers on 

 handling a butterfly or moth consists of a 

 number of microscopic flattened bodies, 

 called scales or feathers, upon which the 

 beautiful colours and opacity of the wings 

 depend, the membranous wing itself being 

 transparent and colourless. 



These scales have always been favourite 

 microscopic objects, both on account of the 

 beauty and variety of their forms, and the 

 curious markings found upon them. The 

 manner in which they are attached is best 

 examined in the wing of a butterfly. Each 

 has a narrow portion at its base, forming a 

 pedicle or stalk. The stalks are implanted 

 into small and short tubes or cups (PL 34. 

 fig. 23 b\ denominated the squamuliferous 

 tubes, the orifices of which are directed 

 backwards. Around the points of attach- 

 ment of the cups to the wings, the surface 



