342 



LAKES AND STREAMS 



sense, the so-called lateral line, which is common to many of the tailed amphibians, 

 and consists of a more or less curved arrangement of small pores in adjoining scales 

 on each side of the body, leading to canals beneath the skin. Fishes, as a rule, 

 swallow their food whole ; some tear or grind it to a certain extent. Very few 

 eat vegetable matter, most species devouring other fishes, or else lizards, molluscs, 

 worms, or other aquatic animals, as well as insects and their larvse. The great 

 majority lay eggs (or spawn), which are usually small, round, soft, and without 

 shells. In most cases the spawn is unfertilised when deposited, the males 

 subsequently pouring the milt over the mass ; but in a few species it 

 is fertilised while in the body of the female. The number of eees is much 



' 



THE PERCH. 



larger than in any other vertebrates, a herring having about forty thousand, 

 a carp two hundred thousand, and the sturgeon and codfish several millions. 

 Fishes spawn only once a year, and usually seek well-sheltered shallow spots for 

 this purpose. At the commencement of the spawning-season they often ascend 

 rivers to their smaller tributaries, as many species can live in both salt water 

 and fresh water. Some fishes are great travellers, others lead an almost 

 sedentary life, staying all their lives in their birthplaces, as is the case with so 

 many of the European fresh-water species. 



Most of the European fresh-water fishes, excluding those of the Adige in the 

 Tyrol, belong to the bony group (Teleostomi) which take their name from the presence 

 of a bony skeleton : and are further distinguished by possessing a gill-cover. Of 

 these the highest in organisation is the perch (Perca fluviatilis), which inhabits 



