356 FISHES 
CHAP. 
(a) Stridulation.—Stridulation as a method of sound-produc- 
tion has been recorded in many Teleosts, and one of the most 
interesting examples occurs in the singular Indian Siluroid, 
(Callomystax gagata).' In this Fish (Fig. 205) the first five 
vertebrae are rigidly connected with one another and with the 
skull, mainly through the union of the neural spines of the third, 
fourth, and fifth vertebrae, and their articulation with the supra- 
occipital bone. The united spines together form a high, laterally- 
compressed lamina of bone, the hinder portion of which is 
vertically cleft into two thin 
plates separated by an in- 
terval sufticiently wide to 
receive the first interspimous 
bone of the dorsal fin. The 
inner surface of each of the 
two plates is traversed by a 
series of about thirty par- 
allel, close-set, vertical ridges, 
while the first interspinous 
bone is similarly ridged on 
both its faces like a double 
Fie. 205. —Stridulating apparatus of Cadlo- 
mystax gagata. is', The first interspinous 
bone, the lower part of which forms the 
double file and fits into the interval between 
file. 
the cleft neural spines xs? and xs? ; is”, is°, 
second and third interspinous bones ; ms°, 
ns‘, ns°, neural spines of the third, fourth, 
and fifth vertebrae ; s1, s*, spine-like rays 
of the dorsal fin ; so, supra-occipital. (After 
Lastly, it may be men- 
tioned that owing to the 
width of the intervertebral 
ligament between them the 
Haddon. ) fifth and sixth vertebral 
centra are articulated by a joint of unusual mobility. The 
action of the mechanism is simple. By the vertical movements 
of the sixth and succeeding trunk vertebrae, with the inter- 
spinous bones which they support, on the rigid structure formed 
by the head and first five vertebrae, the file-like first interspinous 
bone moves backwards and forwards, and, by scraping against 
the ridges on the inner surfaces of the cleft neural spines, gives 
rise to a harsh grating noise, which is particularly unpleasant 
when artificially produced. The lateral movements of the trunk 
in ordinary locomotion do not affect the mechanism: it is only 
when the trunk is alternately flexed and extended in the vertical 
plane that the mechanism comes into play and a noise is pro- 
1 Haddon, Journ. Anat. and Phys. xv. 1881, p. 322; Bridge and Haddon, Phi. 
Trans, 184, 1893, p. 168. 
