BONY FISHES 289 



able hosts to the rivers, spread themselves over whole river basins, and 

 there complete their growth. In their course up the rivers these small 

 creatures defy the strongest currents, and even climb up weirs and 

 waterfalls by means of their slimy skin. It is, of course, evident that 

 the eel must spawn in the sea, since the young come out of the sea, and 

 on the coast of Sicily and Italy eggs belonging to fishes of the eel family 

 have been identified. There is reason to believe that these eggs usually 

 remain at considerable depths. It has been now proved that the Lepto- 

 cephali, small fish of the shape of a ribbon, and of glassy transparency, 

 are the larvae of different species of the eel family, and one of them, 

 L. brevirostris, is believed to be the larva of the common eel. The eel 

 on account of its rich, delicate flesh forms one of our most important 

 food fishes. 



Sub-Order 2 : Fishes in which the Air-bladder is closed 



(Physoclysti) . 



The Perch (Perca fluviatilis). 



(Length up to 16 inches.) 



The perch is found in all clear fresh waters. Like the pike (which 

 see), it is of predaceous habits, and accordingly a rapid swimmer (body 

 laterally compressed). For the same reason the mouth has a wide gape, 

 and is very distensible and armed with teeth. The pharyngeal bones are 

 also armed with teeth, the pharynx wide, the (esophagus dilatable, and 

 the intestine short. Like the pike, it lies in wait for its prey amongst 

 water-plants or under the roots of trees growing along the banks, and 

 hence also its scaly covering reflects the tints of the plant-grown spots 

 which it frequents (greenish with dark transverse bands, under side 

 lighter coloured ; see carp). The perch is also able to assimilate its 

 colour in a few days to that of the ground over which it swims. (Put a 

 perch into a dark and afterwards into a light tinted vessel, and observe 

 the change of colour. This change is still more striking in the case of 

 the Minnow [Leuciscus phoxinus'].) The only formidable enemies of the 

 perch besides man are the otter, the sea-eagle and the heron. The 

 larger kinds of predaceous fish do not venture to attack it, for the 

 perch can inflict severe wounds with the sharp spines of the first dorsal 

 fin — it belongs to the group of spiny-finned fishes (Acanthopteri) — as 

 well as with its gill-covers, which terminate in sharp points posteriorly, 

 and are armed with spines and teeth in front. The eggs of the perch 

 are about the size of poppy- seeds, each contained in a thick envelope, 



