644 



SCANDINAVIAN FISHES. 



Genus GASTEROSTEUS '. 



Body mackerel-like , compressed {greatest depth more than half the Iciif/th af the head), irltlioat other carince than 

 the lateral edges of the belly and the elevation of the lateral line on the hind jiarf nf thr tail: forepart of the 

 hody (in front of the anal spinr) loni/i'r Ihiin thr hind jiart, including the candal fn. Xainber of free spinoas 

 rays in front of the s(ft-raycd dorsal fn less than lo. ]"entral fins inserted at the outer, front corner of the 

 pelvic hones, vhich coalesce n-ith each other in the median line of the belly into a triangular ventral jilatc. 



tajicring behind. Jair-teeth conical. 



The genus of the Sticklebacks contains the most 

 widely-spread of all the Scandinavian iishes. There is 

 hardly a single brook in whicli we fail to see these 

 small and lively creatures swimming merrily about, 

 often within narrow limits which the heat of summer 

 reduces more and more each minute. For economical 

 jjurposes they genei-allv possess far too little importance 

 to interest the practical fisherman, who usually knows 

 them merely by name. The zoologist cannot content 

 himself Avith so slight an acquaintance. To him a 

 knowledge of the Stickleback is quite as important as 

 of its far larger and far more useful fellow, the Salmon. 

 Both are e(iually small fractions in the great series 

 of natural forms which it is his task to investigate, 

 and both are equall)- interesting, equally advantageous 

 subjects of study. When we add to this the wonder- 

 ful instinct of the Sticklebacks, which guides them to 

 an architectural skill exceptional among fishes, we have 

 sufficient grounds for bestowing on them more than 

 usual attention. 



To the sj'steniatist they are also of absorliing in- 

 terest, for the course of development may be traced 

 with especial distinctness in their differences of form 

 and changes of growth. Their relation to the preceding 

 genus has been expressed in a masterly way by Dr. 

 Heincke', in an elucidation of the significance of the 

 variations affecting the dorsal spines in the Three- 

 spined Stickleback. With this object he had examined 

 about 10,000 specimens of the species in question. 



The Three-spined Stickleback is generally furnished 

 — and this is one of its most important characters — 

 with 3 free spinous rays at the dorsal edge in front 

 of tiie soft-rayed dorsal fin. It had long been known, 

 however, that the number of these spinous rays might 



be increased to 4"; and a variety of this kind, with 

 the four spinous rajs comparatively short, had been 

 described l)y CrvU';i; and X'alenciennks'' as a distinct 

 Italian species, Gasterosteas tetracanthus. Heincke found 

 about 1 percent of the Three-spined Sticklebacks that 

 he examined, furnished with four spines; and of this 

 number he examined 61 specimens in order to locate 

 the supernumerary ray. Each of the spinous rays is 

 attached to and articulated, in a singular manner which 

 ^\•e shall describe more fully belo^v, ^vith one of the 

 interspinal plates on the back. These plates are as a 

 rule (fig. l.'iZ and fig. 1.58, B) 6 in number and arranged 



.X,^i-. 



Gastcrosieii^ aculeatus, gymnnriis. Natural size. From 

 It.nlv. After Heincke. 



in a row: 2 small ones just behind tlie head, 2 larger 

 ones, each with a spinous ray, the posterior usually 

 the larger, 1 smaller plate with no spinous ray, and 

 lastly 1 su])porting the iiindinost spinous raj. The 

 largest two of these plates, however, are evidently due 

 to the coalescence of at least 2 plates respectively. In 

 fig. 1.59 we see the anterior one broken up into two 

 ])arts, and in fig. 160 the posterior of them shows the 

 same division. The anterior also rests on the upper 



" The generic name is derived from Artedi, Genera Pisciiiiii, p. 52. 



' Ofvers. Vet. Aknd. Furli. 1889, p. 395. 



' Cuv., Val., Hist. Nat. Poi.?s., vol. IV, p. 491. 



'' 1. c., p. 499. 



