652 
SCANDINAVIAN FISHES. 
about 2 / 5 of its length. All its rays are branched at 
the tip. The peduncle of the tail (the space between 
the dorsal and caudal tins) is twice or three times as 
long as deep. The anal tin begins perceptibly behind 
the perpendicular from the beginning of the soft-rayed 
dorsal tin, but ends almost exactly opposite the ter- 
mination of the latter. The distance between it and 
the tip of the snout is generally greater in the females 
than in the males, the length of the head in all the 
females we have examined, being less than 43 % of 
this distance, in the males more than 44 % thereof. 
The soft-rayed anal tin is preceded by a spinous ray, 
which is usually exactly similar to the last spinous ray 
on the back and joined in the same way to the tin. 
The length (base) of the soft-rayed anal tin varies be- 
tween 14 and 17 % of the length of the body, and 
measures as a rule about 2 / 3 , exceptionally 3 / 4 ", of the 
length of the soft-rayed dorsal tin. It is otherwise 
similar to the latter in structure and form. The ventral 
tins contain two rays, the spinous ray and one shorter, 
soft ray at the hind margin of the tin-membrane. The 
spinous ray is always larger and stronger than any of 
the spinous rays on the back, but otherwise similar to 
the latter and varying under the same conditions as they. 
Thus, its length may vary between more than half (54 
or 55 %) and about one-third (sometimes 29 %) of the 
distance between the first spinous dorsal ray and the 
tip of the snout. The position of the spinous ventral 
ray is subject to the following rules: in the males the 
distance between it and the beginning of the anal fin 
is usually perceptibly less than half of that between it 
and the tip of the snout (exceptionally equal to half 
of the latter), in the females, on the other hand, usually 
considerably greater (60 — 68 % of the distance between 
the ray 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 lie even 
greater than the length of the head, in younger females 
(though more than 5 cm. long) we have found it to be 
only Ys o; f this length, and in the males we have never 
found it to be more than 3 / 4 thereof. The structure 
and position of the pectoral fins are the same as in the 
preceding species, with the same thin-skinned, glossy i 
patch in front of their vertical insertion; but their tips 
are 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 beginning of the anal fin, in the 
females less than 72 % (7 1 — 47 %) of the same distance. 
The caudal fin is straight or slightly forked at the hind 
margin. In all our specimens the 10 6 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 silvery, 
but punctated with brown. The air-bladder is com- 
paratively large, coasts the whole dorsal side of the 
abdominal cavity forward to a line with the first spi- 
nous ray on the back, and sends out, according to 
Kroyer, “from its under surface a canal to the middle 
of the upper surface of the stomach. This canal (pneu- 
matic duct) finally shrinks, however, into a ligament. 
“The most remarkable characteristic of the Three- 
spined Stickleback,” writes Ekstrom, “lies in its varia- 
tions of colour. In winter the body is of a pure sil- 
very white, with the upper part of the head and the 
back blue. In summer the top 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 play of colours. The back first be- 
comes brownish, developing darker, transverse bands, 
and the silvery white sides show a dash of brassy 
yellow. This applies in particular to the females. The 
males at the same time acquire a red spot, which be- 
gins under the head at the meeting of the branchio- 
stegal membranes, 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, 
except the highest 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 
reproduction of a female in her winter dress.” 
“ In exceptional cases also only 62 /. 
b Kroyer found only the 8 middle rays branched. 
