AS AN INDEX OF AGE. 23 



all scales; those of the salmon and lote, for example, do not possess them. 

 They may be limited to one region of the scale, or be present over the 

 entire surface. From a general point of view, they may be divided into two 

 categories: — (1) Those which radiate from the centre of growth towards the 

 periphery are termed radial or radiating grooves (carp, perch). (2) Those 

 which have a direction parallel to the contour of the scale, and therefore 

 perpendicular to the radiating canals, are termed iransverse or cojicentric 

 grooves (Ophidium, whiting). Those two kinds (radiating and concentric 

 grooves) may be present simultaneously in the same scale ; but in the 

 majority of scales only the radiating or radial grooves are found. In most 

 cases they only occupy the anterior region of the scale (perch, pike), but 

 they may occupy the posterior as well as the anterior areas (carp), or they 

 may be present over the entire surface of the scale, anterior, posterior, and 

 lateral (loach, minnow, whiting). When the concentric grooves and radiating 

 grooves are present in the same scale, two cases present themselves : firstly, 

 that in which the two kinds of grooves are found in two different areas of 

 the scale (several Pleuronectids), in which case the radiating grooves exist in 

 the anterior and posterior area, and the concentric or transverse grooves in 

 the lateral areas ; or secondly, that in which the radiating and concentric 

 grooves exist in the same area of the scale, by which means the scale surface 

 is divided up into numerous ^Aates or divisions, which occasionalhj form a 

 regtdar series of plates radiatiiig from the centre to the periphery (Ophidium, 

 whiting, eel). 



While in a general way one may separate the grooves into these two 

 categories, namely, radiating and transverse grooves, there are many scales in 

 which the grooves lose their usual symmetry and affect a more or less 

 irregular arrangement. Sometimes the grooves show up to a certain point 

 the usual radiating arrangement and then anastomose with each other, thus 

 forming on the scale surface a species of plexus of irregular webs (Labridir, 

 Mormyridse). The grooves of the anterior area also frequently anastomose 

 Avith those of the posterior area in the region of the centre of gi'owth 

 (Cyprinus, Labrus). In the herring and shad there are grooves in the anterior 

 part of the scale which originate on the lateral border, and extend across the 

 anterior area, keeping more or less parallel with one another. 



As regards form, the grooves show extremely varied characters : sometimes 

 they take the form of a simple line, resembling a fissure or line of break on 

 the external surface of the scale (herring, shad, transverse grooves of 

 Ophidium, whiting) ; sometimes they appear as a species of ravine, narrowed 

 at the base and cut out perpendicularly at the sides ; at other times they have 

 the appearance of a wide trench of little depth and flat at the base ; some- 

 times the grooves lose their regularity, become narrowed at some points and 

 enlarged at others, constituting species of small depressions (lacules) with 

 sinuous and irregular contours ; sometimes a groove may be interrupted at 

 certain places, and then one has a series of small cavities or depressions 

 (lacules) lying in the same straight line and in the same direction. The 

 edges of grooves are usually irregular and jagged, but they also frequently 

 show rounded lobes, due to the presence of calcareous globules. 



The radiating grooves do not usually extend over the entire distance from 



