]28 FISH GALLERY. 



that at the front of the dorsal fin are three short spines. It 

 is ve^ abundant in all fresh waters, and can be transferred to 

 brackish and sea water without injurious effect. The fish occurs 

 in three varieties ; var. gymnurus, the smooth-tailed variety, with 

 from four to six bony plates behind the gill-cover; var. semi- 

 armatus, the half-armed variety, with from ten to fifteen bony 

 plates behind the gill-cover and a few blunt spines on the side 

 of the base of the tail ; and var. trachurus, the rough-tailed 

 variety, with an uninterrupted series of from thirty to forty bony 

 plates along the side of the body. From recent observations 

 it appears that the variety trachurus is a winter form, the variety 

 gymnurus the same fish in summer dress, when it has discarded 

 its armour, and the variety semiarmatus a fish caught in the 

 spring. In the case of the American Gastrosteus cataphractus 

 the individuals caught in the sea have a complete armour of bony 

 plates, about thirty on each side ; those found in brackish water 

 are half-armoured, with from six to twenty plates, while those 

 found in fresh water have only two or three plates or even 

 none at all. 



The common Stickleback is an active, persistent and greedy 

 little fish. It is very pugnacious and protracted fights are not 

 uncommon ; after the fight the colour of the defeated combatant 

 at once becomes dull, while that of the victor remains resplendent. 

 It is no unusual thing also to see a group of Sticklebacks worrying 

 a fish much larger than themselves by biting little pieces out of 

 the margin of the fins. Sticklebacks do much mischief by 

 devouring the spawn and fry of other fishes. 



In the breeding-season the throat and breast become brilliantly 

 red, particularly so in the males. The male builds a nest by 

 collecting bits of water-weed and leaf- skeletons and cementing 

 them together with a glairy fluid which is secreted in glands 

 opening at the urino-genital aperture, and which hardens into 

 tough threads in contact with water (compare the byssal threads 

 of the bivalve molluscs Pinna and Mytilus, the common Mussel). 

 The nest is constructed prior to mating. A female is then 

 induced to enter the nest and lay her eggs, and when she departs 

 through the other opening, for there are two, one at each end, 

 the male enters and fertilises the eggs. The process is then 



