CHAPTER LI 
THE ORDER OF HALF-GILLED FISHES 
HEM IB R A NO HI. I 
Because of the fact that a few very small 
fishes have less than their rightful number of 
gill-arches, and shoulder-girdles with one bone 
only instead of two, the Order of Half-Gilled 
Fishes has been created. 
The Sticklebacks are very small fishes, only 
a few inches in length, and derive their name 
from the formidable dorsal spines that stand 
upon the back in front of the dorsal fin. We 
have Two-Spined, Four-Spined and Ten-Spined 
observers say that the fish first brings a few 
stems and bits of vegetation, and by means of 
his gelatinous secretion practically ties them 
fast to the upright stalks, to use as a foundation. 
The fish then proceeds to exude its secretion 
and dispose it in commingling rings, vertically, 
around a space sufficiently large for the female 
Stickleback to pass through. In a manner noth- 
ing short of marvellous, a hood-like nest is spun, 
of the fish’s own secretion, which well retains its 
Drawn by J. Carter Beard. 
TWO-SPINED STICKLEBACK. 
Sticklebacks, all three being found in brackish 
water along the Atlantic coast from Cape Ann 
to New Jersey. 
All the Sticklebacks are celebrated for their 
nest-building habits. The abdomen of the male 
fish has been provided with a large gland which 
is “filled with a clear secretion which coagulates 
into threads” when it comes in contact with 
water. At first the fluid is colorless, but after 
contact with water it becomes whitish, and its 
many fibres hang together like strings of spa- 
ghetti. (Ryder.) 
The entire work of nest-building is performed 
by the male Stickleback. It begins by selecting 
a bottom situation, in a gentle current, wherein 
the nest can be attached to two or more stems of 
growing vegetation, and anchored fast. Some 
shape for some weeks. In this^ the female de- 
posits her eggs, all the time jealously watched 
by the male, to prevent her from eating them! 
The male guards the eggs unti 1 they are hatched, 
and it is said that if the current flowing through 
the nest does not meet his views as to strength, 
the fish increases the volume of it by moving its 
pectoral fins to and fro. Sticklebacks are some- 
times kept in aquaria in order that they may 
show their wonderful intelligence in nest-building. 
The Two-Spined Stickleback 1 will serve 
as a type for the whole Order. It is only about 7 
inches long, and has no commercial value. It 
is said to occur in cjuiet brackish waters along 
our coast, but is seldom brought into notice out- 
side of aquaria. 
1 Gas-ter-os'te-us a-cu-le-a'tus. 
