208 



THE FRESH- WATER FISHES OF EUROPE. 



curve, and again descends even more suddenly towards the tail, where the 

 height is scarcely one-third of the height of the middle of the body. 



The dorsal fin begins in the middle of the length of the body ; the anal 

 commences before the termination of the dorsal, and both have the longer rays 

 equal to half the height of the fish. The vent is placed midway between the 

 anal and ventral fins, and is covered with scales which extend round it like a 

 sheath. The ventral fin reaches back to the anal. The ventral and pectoral 

 fins are equal ; the caudal is evenly-lobed and moderately notched. 



The scales are thin and elongated, approaching a sub-oval form their 

 longer diameter is equal to that of the eye in the adult fish. The scales in the 

 young, according to Fatio, are relatively only one-fourth or one-third as large as 

 those in the adult. The scales partially overlap each other, and are marked 



Fig. 114. RHODEUS AMARUS. 



with radiating lines, ten to thirty-five in number. The free edge is rounded ; 

 and the attached margin is sub-convex. The scales on the back, breast, 

 abdomen, and root of the tail, are smaller and more circular than those on the 



sides. In the lateral line the scales are 

 transversely wide, and only from one 

 or two to seven are perforated. 



The accessory gills are free and 

 pectinate. The entire upper division 

 of the gill-arches is covered with mem- 

 brane, and it has been supposed that 

 this separation of the mouth aperture 

 and the peculiar respiration it implies 



may not be unconnected with the tenacity of life for which this fish is 

 remarkable. Fig. 115 shows the pharyngeal teeth. 



The colour varies with sex and season of the year. The males at spawning- 

 time in summer develop every year two circular patches of warty tubercles 

 above the mouth, which periodically disappear, a character in which they are 



Fig. 115. PHAHYNGEAL TEETH OF RHODEUS 

 AMARUS. 



