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, 

 (Gallomystax 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 sufficiently wide to 

 receive the first interspinous 

 bone of the dorsal fin. The 

 inner surface of each of the 

 two plates is traversed by a 

 . j series of about thirty par- 

 allel, close-set, vertical ridges, 

 n.s$ f while the first interspinous 



FIG. 205.-Stridulating apparatus of Callo- bone j g similarly ridged on 



mystax gagata. is 1 , The first interspmous 



bone, the lower part of which forms the both its faces like a double 



double file and fits into the interval between fi i j f i - f i 



the cleft neural spines * and ns> ; is\ is 3 , lLl6 ' WMJ' " ma 7 l 



second and third interspinous bones ; ns 3 , tioned that Owing to the 



ns\ ns 5 , neural spines of the third, fourth, iji r 1.1 i 1.1 i 



and fifth vertebrae ; s\ a spine-like rays wldth of ^6 mtervertebral 



of the dorsal fin ; so, supra-occipital. (After ligament between them the 



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, Phil. 

 Trans. 184, 1893, p. 168. 



