iWi-> 



SCANDIXAVIA.N FISHES. 



about ^ ^ of its lonjztli. All its rays aiv hi'aiiched at 

 the ti|i. The iicduiicle of the tail (the space between 

 the dorsal and caudal fins) is twice or three times as 

 long as deep. The anal fin Ijegins perceptil>ly behind 

 the perpendicular from the beginning of tlie soft-rayed 

 dorsal fin, but ends almost exactly opposite the ter- 

 mination of the latter. Tiie distance between it and 

 the ti]i of tile snout is generally greater in the females 

 than in the males, the length of the head in all the 

 females ^\e ha\c examined, being less than 43 % of 

 this distance, in the males more than 44 % thereof. 

 Tlie soft-rayed anal tin is preceded by a spinous ray, 

 which is usually exactlj^ similar to the last spinous ray 

 on the back and joined in the same way to the fin. 

 The length (Itase) of the soft-rayed anal tin varies be- 

 tween 14 and 17 % of the length (-)f the body, and 

 measures as a rule about ^j, exceptionally ' i "> of the 

 length of the soft-rayed dorsal fin. It is otherwise 

 similar to the latter in structure and form. The ventral 

 tins contain two rays, the spinous rav and one shorter, 

 soft ray at the hind mai-gin of the fin-membrane. The 

 spinous ray is always larger and stronger than any of 

 the s])inous rays on the back, but otherwise similar to 

 the latter and varying under the same conditions as they. 

 Thus, its length may vary Ix'tween uku'c tlian half (54 

 or 5n %) and about one-third (sometimes 29 %) of the 

 distance between the tii'st spinous dorsal vaj and the 

 tip of the snout. Tlie position of the spinous ventral 

 ray is subject to the following rules: in tlie males the 

 distance between it and the beginning of the anal tin 

 is usually perceptibly less than half of that between it 

 and the tij) of the snout (exceptionally equal to half 

 of the latter), in the females, on the other liaiid, usually 

 considerably greater (60 — 68 % of the distance between 

 the rav and the tip of the snout), though the young 

 females come nearer the males in this respect, or are 

 even similar to them. The same distinction of age and 

 sex may also be observed in the relation to the length 

 of the head: in old females the distance between the 

 spinous ventral ray and the anal fin may be even 

 greater than tlic length of the head, in j'ounger females 

 (though more than o cm. long) we have found it to be 

 onl)- V5 of this length, and in the males we have never 

 found it to be more than '7i thereof. The structure 

 and position of the pectoral fins are the same as in the 

 preceding species, with the same thin-skinned, glossy 



" In exceptional cases also only 62 %. 



' Kroyer found only Ihe 8 middle rays branclicd. 



patch in front of their vertical insertion; but their tips 

 ai'e more sharply truncate. Their length varies between 

 about 13 and 17 % of that of the body, measuring in 

 the males, according to our measurements, more than 

 72 % (73 — 90 %) of the distance between the spinous 

 ventral ray and the begitining of the anal fin, in the 

 females less than 72 % (71 — 47 %) of the same distance. 

 The caudal fin is straight or slightly forked at the hind 

 margin. In all (^ur specimens the 10'' middle rays are 

 branched, the others simple. The length of the fin at 

 the middle is about equal to the postorbital length ot 

 the head. 



The internal organs are similar to those of the 

 Fifteen-spined Stickleback. The peritoneum is silvei-y, 

 but punctated with brown. The air-))ladder is com- 

 paratively large, coasts the whole dorsal side of the 

 abdominal cavity forward to a line with the fii'st spi- 

 nous ray on the back, and sends out, according to 

 Kroyer, "from its under surface a canal to the middle 

 of the u])per surface of the stomach." This canal (pneu- 

 matic duct) finally shrinks, however, into a ligament. 



"The mo.st remarkable characteristic of the Three- 

 spined Stickleback," writes Ekstrom, "lies in its varia- 

 tions of colour. In winter the body is of a yiui'e sil- 

 very white, with the upper jwrt of the head and the 

 back blue. In summer the tO]) of the head and the 

 whole of the back down to the lateral line are blackish 

 gray. When the spawning-season sets in, the fish ex- 

 hibits a surprising plav of colours. The back first l>e- 

 comes brownish, developing darker, transverse banrls, 

 and the silvery white sides show a dash of brassy 

 yelhnv. This applies in jjarticular to the females. The 

 males at the same time accpiire a red spot, which be- 

 gins under the head at the meeting of the branchio- 

 stegal nienibranes, and which expands rapidly, the red- 

 dish tinge usually extending throughout the lower part 

 of the fish, from the tip of the lower jaw to the vent. 

 The extent of this red colour varies in different indi- 

 viduals. In some cases it rises up the sides a little 

 above the lateral line; in others the whole body is red, 

 excejit the liigliest part of the back, which is then 

 reddish brown, and the forehead, which is always of a 

 deep bluish-green colour. The iris is of a handsome 

 green. We have represented a male in this attire in 

 Plate XXVIII, fig. 2, and fig. 1 in the same plate is a 

 rei)roduction of a female in her winter dress.' 



