384 



TEGUMENTARY ORGANS 



Fig. 309. — Scale of the Roach (Leuciscus). 

 section ; B, surface. 



A, 



of their surface are bare and hard, the anterior third becomes gradually 

 softer from the prolongation of the integument over it. The posterior 



surface continues hard up to its 

 sharp edge, but it is supported 

 below by a soft thick layer of 

 integument, which passes on to 

 the anterior soft coat of the 

 scale behind, and thus masks 

 the real overlapping of this scale 

 by the posterior edge of that 

 which precedes it {fig. 310. B). 



The surface of the scale is 

 shining and glassy. It is marked 

 by a medium ridge, whence it 

 shelves upon each side, and by 

 an elegant sculpturing produced 

 by raised, hard ridges of the 

 same nature, which radiate from 

 the margins centrally for about 

 a fourth of the semidiameter of the scale. In the region within 

 this zone, the ridges gradually lose their regularity, the radiating lines 

 anastomosing with one another and forming an elegant polygonal 

 network. The soft surface of the integument of the anterior portion 

 of the scale, is raised into many 

 minute papillae {fig. 310. A, a), 

 which may be followed for some 

 distance on to the hard portion. 

 Furthermore, it exhibits scattered 

 round spots,with projecting centres 

 of the same appearance as the 

 ridges, and like them feeling hard 

 to the touch. 



If a section of the scale be 

 made {fig. 310. B), its under sur- 

 face will be found to have a con- 

 cavity corresponding with the con- 

 vexity of the upper. If the section 

 has passed through one of the 

 ridges, it is seen that the osseous 

 tissue of the scale is of two kinds : 



a superficial homogeneous-looking, dense, comparatively thin layer, and 

 a deep, thick, laminated portion. If traced from the centre of the scale 





Fig. 310. — Scale ot Sturgeon. A, one of the 

 detached tubercles highly magnified ; B, 

 the entire scale. 



