402 



AMERICAN MUSEUM OF NATURAL HISTORY 



Dermal Skeleton — Cont'd. 

 ctenoid scales, once thought fundamental, 

 have been gradually shown to be unimportant. 

 Cycloid scales may be defined as those which 

 possess a smooth posterior margin; and ctenoid, 

 those in which this margin is produced into a 

 series of small spines. Reduced to the simplest 

 teipms, as shown by Cockerell & Moore (1910.2) 

 an,d independently corroborated by Hase (A. 

 1911.1); when the growth-rings or circuli are 

 parallel with the margin, the scale is cycloid. 

 When, however, the growth-rings strike the 

 posterior scale margin at a right angle or per- 

 pendiciilarly, their truncated ends form tooth- 

 like spines and the scale is ctenoid . Each growth- 

 ring may produce a spine or several may unite 

 to form one spine (Hase) . 



Mandl (L. 1839.2), Vaillant (L. 1875.2) and 

 Tims (H. W. 1905.1) erroneously believed the 

 " teeth " of ctenoid scales to be homologous 

 with the spines of the denticles of sharks. The 

 correct view that they are merely projections 

 of the posterior scale border, first propounded 

 by Agassiz (L. 1840.3) in opposition to Mandl, 

 has been held also by Baudelot, Carlet, Hofer, 

 Klaatsch, and others. 



Morphology of scales 



Papers primarily on the development of 

 scales, both cycloid and ctenoid, including 

 their microscopic structure. I^Baudelot 

 E. 1873.4; Carlet, G. 1878.1, 1879.1 

 •Gmnelius, A. 1913.1; •Hase, A. 1907.1 

 Hofer, B. 1889.1; •Nusbaum, J. 1907.1 

 RosSn, N. 1915.1; Tims, H. W. 1905.1 

 Ussow, S. A. 1897.1. 



Although the CharacinidcE ordinarily 

 possess cycloid scales. Gill enumerates four 

 subfamilies with ctenoid scales. Gill, T. N. 

 1896.11. 



Each scale of the lateral line is pierced by 

 a pore of the lateral line canal. These refer- 

 ences describe the lateral line scales in the 

 following. — Scopelidce. Cohn, L. 1907.2. 

 — Mugil. F6e, F. 1869.1. — ScimnidcB. 

 Sauvage, H. E. 1877.4. — Serranidce. 

 Vaillant, L. L. 1874.2. 



Johnstone describes a flounder having 

 part of the scales spinulated. Johnstone, 

 J. 1904.1. , 



The Plectognathi including the Sclero- 

 dermi, containing the Trigger-fishes (Balis- 

 tidce), File-fishes (Monacanthidw), Globe- 

 fishes (Tetrodontidce) , and Porcupine fishes 

 (Diodontidce) , have the body encased in 

 heavy plate-like scales or, as in the Porcupine 

 fish, Diodon, have the scales produced into 

 sharp spines. Consult Dareste, C. 1850.2; 

 Hertwig, O. 1876.1 (vol. vii); Bollard, 

 H. L. 1853.1, 1860.1; •RosSn, N. 1912.1 

 (iii) ; Kaschkaroff, D. N. Add. 1914.1. 



The Trunk-fish (Ostracion) is encased in 

 a rigid cuirass resulting from the union of 

 rhomboidal plates placed side by side, 

 which possess an inferior layer of a ,homy 

 nature and a superior layer of osseous 

 substance. HoUard, H. L. 1857.2. 



The Lophobranchii, including the Pipe- 

 fish^ (Syngnathus) and the Sea-Horse 

 (Hippocampus) , have the body protected by 

 a series of dermal scutes forming rings. 

 See Hoyer, H. 1901.1; Kasanzeff, W. 

 1906.1; and Schaff, E. A. 1886.1. 



The John Dory (Zeus faber) possesses a 

 series of bony plates or spines along the 



base of the median fins. For their, number 

 and arrangement, see Byrne, L. W. 1902.3. 



The scales of Centriscus possess sharp 

 spines and were thought to he intermediate 

 between denticles and scales. Hertwig, O. 

 1876.1 (vol. vii, p. 15); Vaillant, L. L. 

 1888.1. 



Separate papers have appeared de- 

 scribing the structure of the scales in the 

 following forms. ■ — Cyclopterus. •Hase, 

 A. 1911.2. — Anguilla. Jourdain, S. 

 1880.1. —Zoarces. Quekett, J. T. 1852.2. 

 — Gobius. Vaillant, L. L. 1875.2. — 

 Chaunax. Vaillant, L. L. 1888.1. — 

 Perca, Gobius, and Platessa. Winther, G. 

 P. 1872.1. 



Scales of the American and Asiatic 

 Cyprinidoe. Cockerell, T. D. & Allison, E. 

 M. 1909.1; CockereU & Callaway, O. 

 1909.1; Cockerell & Moore, E. V. 1910.1. 



Scales of Dipnoi 



In the recent lungfishes, the scales are cycloid 

 and overlapping and sunk deep within the 

 dermis. 



References are Cockerell, T. D. 1911.7; 

 Gilnther, A. (Neoceratodus) 1871.4; 

 Klaatsch, H. 1890.1; Kolliker, R. A. 

 (Protopterus) 1860.1; Wiedersheim, R. 



E. 1880.4. 



Chemical composition ot denticles 

 and scales 



The scales of Teleosts are composed chiefly 

 of mineral matter, collagen, and ichthylepidin, 

 the latter forming about one-fifth of the organic 

 substance. 



Ichthylepidin, which is close to elastin, was 

 discovered by Morner. It is insoluble in hot and 

 cold water as well as in cold dilute acids or 

 alkalies, but on boiling with the latter it dis- 

 solves. It responds to Millon's reagent and 

 blackens, from loosely combined sulphur, when 

 boiled with an alkaline solution of lead acetate. 



Morner found it to occur in the scales of 

 twelve species of Teleosts examined but found 

 it lacking in Lepidosteus. Green & Tower, 

 examining the scales of thirty-five species of 

 Teleosts belonging to widely separated families, 

 found it to occur in all except the ocean sun- 

 fish (Mola) and the puffer (Spheroides) . They 

 found that it occurs in Acipenser. 



The denticles of Elasmobranchs, however, 

 have collagen as their organic basis. Four 

 species of sharks and rays examined showed no 

 trace of ichthylepidin. 



Earlier papers on the composition of 

 scales. Green, J. 1858.1-1862.1; Weiske, 



F. 1883.1; Wicke, W. 1853.1. 

 Jackson records the presence of fluorine 



in the scales of Lepidosteus. Jackson, C. T. 

 1856.2. 



Nature and occurrence of ichthylepidin. 

 Green, E. H. & Tower, R. W. 1902.1, .2; 

 Morner, C. T. 1898.1, 1902.1. 



Economic uses of shark and 

 other fish skins 



Formerly pieces of sharks' skin with the at- 

 tached hard denticles (shagreen) , were used by 

 cabinet makers for polishing wood and ivory. 

 At present the production of other abrasives 

 has largely resulted in their disuse. Such " sha- 

 green " was very durable, a piece outwearing 

 many sheets of sandpaper of equal area. 



Similarly the dried or tanned skins of fishes 

 have been used to some extent as ornamental 

 leathers for covering small ornamental objects 



