l-'IfTKEN-Sl'INEI) STICK LKUACK. 



641 



(if 10" simple rays ol' CairK iiiiiCorui Icngtli, tlioiigli 

 the iiiiddlf (UK'S mi'c shiik-w Ii;iI luno-er than the outer, 

 the ti|i 1)1' tile tii\s, when iUvv are tdlileti, lieiiiL;' thus 

 e\eiil\-, hut sharply roumh^d. Wheti expanded these 

 tins are Ian-shaped. Their hase is almost jiei'pendieular, 

 and hy the i^ri-at expansion of the shouhh'r-lilade and 

 the eoracoid bone is removed I'arther than usual from 

 the ( laviclc, leaving an even pattdi, coNcred with glossy 

 skin, in front of it. The length ot the pectoral fins is 

 gen(!ralh about ecpial to the base of the soft-rayed 

 dorsal or the anal (in, ancl is usually somewhat greater 

 in the males than in tlie females, varying between 

 about 10 and 12 % of the length of the body. 



The ventral tins lie a little liehind the ndddle of 

 the pelvic bones and a little behind the end of the first 

 third'' of the bod}-. 'I'liey are made up of one spinous 

 ray, which is distinctly longer than (sometimes nearly 

 twice as long as) any of the other spinous i-ays, and 

 behind this yn\ the\- have a triangular tin-membrane, 

 set obli(piely inwards and backwards, and containing 

 in its posterior (inner) part two small, soft rays, the 

 last of which is in most eases difficult to detect. Like 

 all the other s])inous rays, that of the ventral tins is 

 also granulated throughout the greater part of its length, 

 with smooth tip; but in this species all the sjjinous 

 rays are without lateral spines and denticles. 



The onlv external difference that we have been 

 able to discover between the sexes of tliis species, is 

 that pointed out by Lilljebokg, namely that the pec- 

 toral tins are generally longer in the males than in the 

 females; and even this is faint. This uniformity is 

 highl)- remarkable, for in our other Sticklebacks tiie 

 difference between the sexes is striking enough, even 

 in the external form. 



The peritoneum is white with a silvery lustre, but 

 dotted with black, \\-hich is often the predominant co- 

 lour on the dorsal side of the alxlominal cavity. The 

 intestinal canal is simple and short. Just behind the 

 diaphragm the oesophagus, which is lined with longi- 

 tudinal folds, passes into the stomach, tlie inside of 

 which is reticulate, and which extends scarcely half-way 

 along the abdominal eavitv, to about a line with the 

 hind extremity of the interclavicles, where it is bounded 

 from the intestine bj' a strong and muscular contrac- 

 tion. The inside of the intestine is thickly lined with 



\illi, ai'ranged in obliciue, traiis\erse series. in a 

 straight diri.'ction, and with a breadth almost e(pial to 

 that of the stomach, but growing narrower behind, the 

 intestine extends almost to the end of the abdominal 

 cavity, where it bends in a sharp curve obli(|Uidy u|>- 

 wards and forwards, soon to return in a cui'N'e no less 

 sharp backwards and downwards to the vent. The only 

 trace of pyloric appendages that we have been able to 

 discover, is an extremeh' short process, dii'eeted baek 

 towards the stomach, on the intestine just beiiind the 

 pylorus. 



The li\er lies in the foi-m of an undivided mass 

 below and along the sides of tlie (esophagus and sto- 

 mach, with a blunt point in a downward and forward 

 direction towards tlie union of the interclavicles. On 

 the left side it has a short lateral lobe, which does not 

 extend further back than the main lobe; but the lobe 

 on the right side is longer, and follows the intestine 

 for aliout half of its anterior, straight part, or a little 

 further. At the end of the middle lobe, under the ter- 

 mination of the stomach, a little to the right, lies the 

 gall-bladder, and on the left side, above the end of the 

 stomach, the spleen. The air-bladder is situated in the 

 posterior part of the abdominal cavity, and its anterior 

 extremity lies above the end of the stomach. 



The ovaries and testes are paired ancl saccate. The 

 former at least, with their comparatively lai-ge and few 

 eggs — KiiOYER estimated their maximum number at 

 300 — occupy the greater part of the abdominal cavitj- 

 during the spawning-season. 



In coloration the Fifteen-spined Stickleback is one 

 of our most beautiful tishes, though under the influence 

 of mental agitation, of terror for example, it often 

 suddenly loses its beauty and brightness of colour, and 

 does not regain them for a long time. The up])er part 

 of the body is olive green, shading into brown, the 

 lower yellowish \\ith white, silvery belly. The sides 

 are, as it were, transparent, sho^ving glimpses of the 

 spinous processes of the vertebra? in the form of dark, 

 transverse, i>arallel streaks. Below the lateral line, on 

 a ground of lustrous silver, lies a row of large, crescent- 

 shaped and oval, olive green spots, which grow smaller 

 behind and iinall}' disappear on the tail. A dark brown 

 liand runs along the side of the head from the cor- 

 ner of the mouth to the base of the jjectoral tin. 



" Sometimes 9: exceptionally 11. 



The distance between the ventral spine and tlio lip of tlie snout varies in different individn 

 length of tlie Iiodv. 



Is between about 34 and 37 



