TEN-SPINED STICKLEBACK. 
659 
sometimes even the greater number of them may lie 
wanting. They do not stand at right angles to the 
back, but lean alternately towards the sides. They are 
also set, not in a straight line, but in a zigzag (v.w). 
They are subulate in form, somewhat curved but only 
slightly widened at the base, with sharp points and 
smooth edges. In size they are fairly equal, though the 
hindmost ray is generally somewhat larger than the 
others" and equal in length to the spinous ray in front 
of the anal tin. All of these spinous rays are usually 
shorter than the diameter of the eyes; but the anal 
spine may sometimes equal this diameter in length. 
Each of them has a small, triangular fin-membrane be- 
hind it. In this species too, the ventral spines are the 
largest, their length varying between 2 /' 5 and l / i of the 
distance between the first dorsal spine and the tip of 
the snout. At the outer margins, at least in full-grown 
specimens, they are usually granulated or even spiny 
with osseous tubercles arranged in several rows. Their 
articulations are constructed in the same manner as in 
the preceding species. 
The pelvic bones are narrower than in the Three- 
spined Stickleback, and the sinus in their anterior mar- 
gin is deeper but narrower. Their upright lateral pro- 
cesses are somewhat broader and more obliquely cut at 
the top. The interclavicles are also narrower than in 
the preceding species, but of about the same length, 
the pelvic bones lying entirely behind the perpendicular 
from the insertion of the pectoral fins. 
The head as well as, in most cases, the whole body 
is more elongated (shallower) than in the Three-spined 
Stickleback; but its relative length is about the same, 
being on an average about 1 / 4 of that of the body. Its 
structure is also the same as in the Three-spined Stickle- 
back, with the exception of the character that lies in 
the above-mentioned arrangement of the branchiostegal 
membranes. 
The soft-rayed dorsal and the anal fins are also of 
a low, triangular form. The first ray in each of them 
is simple but distinctly articulated. They are fairly 
analogous in position, the beginning of the dorsal fin 
never lying in front of the perpendicular from the hind 
part of the vent. The base of the soft-rayed dorsal fin 
is always perceptibly shorter than the head, but varies 
between 20 and 24V 2 % of the length of the body. 
The length of the base of the anal fin varies between 
about 16 and 1 9 1 / 2 % of that of the body. 
The hind margin of the caudal fin is straight, some- 
times slightly forked or even convex, an indication of 
the transition to Gastrcea. Its length at the middle is 
always perceptibly less than the postorbital length of 
the head. The pectoral fins are similar to those of 
the Three-spined Stickleback both in form and rela- 
ive size. 
The internal organs resemble those of the Three- 
spined Stickleback; but the air-bladder is somewhat 
narrower. K rover found some instances to corroborate 
Cuvier’s observation to the effect that the intestine runs 
from the stomach straight to the vent, instead of pre- 
viously forming a circular coil, as it generally does 
both in this species and in the two preceding ones. 
The relation between this species and the Three- 
spined Stickleback is of especial interest when we con- 
sider the external differences of. growth and sex, which 
show that the Ten-spined Stickleback represents partly 
the earlier (lower) stages of development and partly 
the male characters. The following table of averages 
contains the changes of growth most important in this 
respect, together with the sexual differences especially 
conspicuous in the Ten-spined Stickleback. 
Average in 
10 speci- 
mens of 
Gcister- 
osteus 
pungitus. 
14 speci- 
mens of 
Gaster- 
osteus 
aculeatus. 
8 speci- 
mens of 
Gastrcea 
spinachia. 
Obs. 
Length of the body expressed, in millimetres... - 
48.7 
62.7 
107. 0 
— 
Longitudinal diameter of the eyes in % of the length of the snout 
102.3 
91.8 
42.7 
juv. sen. 
Postorhital length of the head in % of its total length 
49.8 
43.2 
43.8 
d 
O 
A 
> 
Length of the base of the anal fin in % of the distance between the anal spine and the tip of the snout.. 
33 9 
24.7 
23.3 
juv. sen. 
» » s head in % of the distance between the first dorsal spine and the tip of the snout 
93. o 
79.o 
100.2 
juv. sen. 
n n n n ?? n 11 5 ? ii ii ii anal ii ii ii ii ii ii ii - 
45.9 
-ll.o 
49.8 
d*>9 
Postorbital length of the head in % of the distance between the first dorsal spine and the tip of the snout 
4(3.4 
34.3 
43.9 
tf>9 
Distance between the ventral spines and the anal spine in % of the length of the head. ... 
79.3 
89.3 
44.9 
cf <9 
„ „ „ „ ,, „ „ „ „ „ „ „ ,, distance between the ventral spines and the tip of the snout 
55.2 
58.fi 
30. o 
<? <9 
ii ii ii ii ii ii ii ii ii i ' ii ii ii ii ii ii spine ,, ,, ,, ,, y, 
35.9 
36.9 
22.9 
c? < 9 
EkstrSm (Vet. Akad. Handl., 1. c.), however, found the second ray longest and the hindmost shortest 
