290 TEXT-BOOK OF ZOOLOGY 



the surface of which is glutinous, so that the eggs adhere together in 

 strings or loose clumps, and these are attached generally to reeds or 

 water-weeds. 



The Perch -Pike (Lucioperca sandra), a nearly -related species, 

 resembles the perch in habits. It inhabits rivers and lakes with stony 

 banks in Central and Eastern Europe, but does not occur in Britain. Its 

 colour is usually a dirty grey, the upper side being marked with dark 

 spots and stripes, especially in the young fish, which are still in need of 

 protection (compare with pike and perch). It is of slender, elongated 

 shape, intermediate between the pike and perch (whence its name), and 

 a swift and nimble swimmer. The mouth is adapted for a predatory 

 life, being armed with fang-like teeth (see pike). It attains to a length 

 of about 4 feet, and its flesh is much esteemed. 



Stickleback (Gastrosteus). 



The Common or Three-Spined Stickleback (O. aculeatus) is a well- 

 known inhabitant of pools, ponds, ditches, as well as of lakes and marine 

 inlets, in the northern portions of the Old and New World. It is fre- 

 quently found in very large numbers, and is a pretty little fish, ranging 

 from 1£ to 3J inches in length. Its slender shape indicates that it 

 swims nimbly ; it feeds on young fishes, insect larvae, etc. The male at 

 the spawning season exchanges its silvery colour for a more handsome 

 " wedding-dress " (compare with birds). The back now assumes a vivid 

 green colour, the under side a brilliant red. The body is protected by. 

 bony scutes instead of scales. The ventral fin only consists of one hard 

 spine and one soft ray, while three similar spines are found in front of 

 the dorsal fin. These are erected with lightning-like rapidity at the 

 approach of danger, and maintained for hours long in their upright 

 position. Since, however, the muscles by which these spines are raised 

 would soon become fatigued, a special catch mechanism is provided for 

 keeping the spines in their erect position. By pressing the tip of the 

 spine we fail to fold it down ; this, however, is easily effected by pressing 

 with a needle a particular spot at the base of the spine, by which means 

 the catch mechanism is released. On account of these adjustable spines 

 (compare with perch) the little fish has few enemies, and therefore is 

 often very abundant. At the beginning of the spawning season the 

 male constructs a nest of about the size of a walnut at the bottom 

 of the water out of roots and water-plants, and then compels first one 

 of the females to deposit its eggs (two or three) in it, afterwards a 

 second female, and so on, until a sufficient number of eggs have been 

 accumulated. The male now takes up its place close in front of the 



