648 
SCANDINAVIAN FISHES. 
Storm, N. Viol. Selsk. Skr., Trondhj. 1883, p. 15; Mob., 
Hoke, Fiscli. Osts., p. 66; Lillj., 6'v., Norg. Fisk., vol. I, 
p. 343; Mob., Nature, vol. XXXIX, No. 9I>8 (Dec. 13, 1888) 
Hcke, dfvers. Vet.-Akad. Forli. 1889, p. 395. 
Gcisterosteus biaculeatus, Shaw (ex. Penn.) Gen. Zool., vol. 
IV, p. 608. 
Gasterosteus trachurus + G. gymnurus ( leiurus ) + G. argyropo- 
mus + G brachycentrus + G. tetracanthus + G. noveboracensis 
+ G. niger , Cuv., Regn. Anim., ed. 2, tom. II, p. 170; 4- G. 
semiarmatus + G. semiloricatus , Cov., Vat.., Hist. Nat. Poiss., 
vol. IV, pp. 493 et 494; G. loricatus + G. dimidiatus, Reinh., 
D. Vid. Selsk. Math. Naturv. Afh., VII (1838), pp. 114 et 
119; G. aculeatus + neustrianus 4- semiloricatus 4- semiarmatus 
4- leiurus + Bailloni 4- argentatissimus + elegans , Blanch., Poiss. 
■ d. eaux douces Fr., pp. 213 — 236; G. aculeatus 4- ponticus 
+ noveboracensis + suppositus + obolarius (?) 4- loricatus + niger 
+ serratus 4- neustrianus 4- semiarmatus + semiloricatus + texa- 
nus 4- leiurus + Bailloni 4- algeriensis 4- plebeius 4- inopinatus 4- 
argentatissimus 4- elegans 4- islandicus + biaculeatus + microce- 
phalies + argyropomus 4- brachycentrus 4- tetracanthus 4- spinu- 
losus , Sauv., Nouv. Arch. Mus., tom. X, pp. 9 — 25; G. 
microcephalus 4- biaculeatus 4- atkinsii (ex Bean) 4- aculeatus , 
Jord., Gilb., Bull. U. S. Nat. Mas., No. 16, p. 395. 
Obs. The great number of nominal species that have been estab- 
lished, according to the above list of synonyms, in the endeavour 
to elucidate the inconstancy of form among Three-spined Stickle- 
backs, is merely a significant token of the lengths to which this in- 
constancy may run in a species that sometimes occurs in enormous mul- 
titudes, is found in far distant localities both in salt water and in fresh, 
and both in form and colour shows marked sexual distinctions. 
The Thi •ee-spined Stickleback attains a length of 
at least about 9 cm. Our largest specimen is a female 
from Greenland which measures rather more than 91 
mm. from the tip of the snout to the end of the middle 
rays of the caudal tin, or 93 mm. from the tip of the 
lower jaw to the end of the outer caudal rays". The 
form of the body reminds us strongly of the Horse- 
Mackerel, being fusiform with strong lateral compression. 
The body is deepest across the pelvis at the articulation 
of the ventral spines, where the depth is about 1 / 5 of 
the length of the body, varying individually between 
18V 2 and 227 2 % thereof. The thickness at the same 
spot is about half the depth, varying individually be- 
tween 44 and 57 % thereof. Except during the spawn- 
ing-season, when the organs of generation become tumid 
and render the body more terete, the thickness is almost 
uniform from the eyes back to the strongly compressed 
base of the caudal fin, the sides being flat throughout 
the forepart of the body, but with sharp Carinas on 
their posterior parts, except in the variety gymnurus, 
which is without caudal plates, and in which the sides 
of the tail are also flat. The dorsal profile between the 
head and the soft-rayed dorsal fin and the ventral pro- 
file between the head and the anal fin are usually com- 
paratively straight or only slightly convex, while the 
upper and lower contours of the head in front and of 
the tail behind are more sharply convergent. Some- 
times, however, especially in the females, which gene- 
rally show a deeper form of body, the entire upper and 
lower profiles of the body run in unbroken curves. The 
external form is also affected to a considerable extent 
by the more or less advanced development of the co- 
vering of plates, this being the origin of most of the 
numerous different names by which the species has 
been known. 
The whole covering of plate-armour shows fairly 
great individual variations both in extent and in strength. 
In its strongest form it consists of comparatively thick 
osseous growths in the skin, externally resembling Ga- 
noid scales, granulated and striated by grooves and 
ridges, the latter rough with small granules. But, as 
Heincke has remarked, both the thickness and the rough- 
ness may be reduced, to the greatest extent, as a rule, 
in the Three-spined Sticklebacks that inhabit brackish 
or fresh b water, or belong to more southern regions. 
Still forms with extremely reduced plate-armour also 
occur in the Arctic regions, as for instance in Green- 
land, where the Sofia Expedition of 1883 took a number 
of small specimens of the gymnurus form in a lake near 
Ritenbenk (North Greenland). These specimens, like the 
Italian argyropomus , have only three plates on each side 
of the body, namely the three that adjoin the ascending 
lateral disk of the pelvic bones. 
The plate-armour of the back we have already exa- 
mined for the most part, and we need only add that 
here, as in the Fifteen-spined Stickleback, the soft-rayed 
dorsal fin rests on a row of interneural plates (here 
about 13, i. e. — excluding the plate of the last spinous 
ray — one for each ray and one more behind the fin). 
This statement also applies to the anal fin, which gene- 
rally has 11 interhsemal plates at the base, the first 
supporting the spinous ray and the last two usually 
a Thus almost exactly equal to the largest specimen in Copenhagen Museum, according to Hansen (Zool. Dan., 1. c.). According to 
Pallas it attains a greater size. His G aster acanthus cataphractus from Kamchatka seems to be simply the typical Three-spined Stickleback, 
but is stated to attain a length of 122 mm. (longitudine pollicum sesquiquinque). Cf. also Tilesius, Mem. Acad. Petersb., tom. Ill (1809 
— 10), p. 226. 
b Already remarked by Kr0Yer (1. c., p. 180). 
