EAR OF THE SQUETEAGUE. 1215 



trace of such a structure. This condition has been reported already by Retzius 

 (188 1, p. 215) for 20 of the t,t, species of teleosts that he studied. Among these 

 there were 15 that belonged to the same order as the squeteague, the Acanthop- 

 teri, and in only i of these 15, Gasterosteus, was the sacculus found to com- 

 municate with the utriculus. In this respect, then, the squeteague is like the 

 great majority of the acanthopterous fishes thus far examined. 



The utriculus is a slender sac which lies dorsal to the sacculus and is of 

 about half the length of that structure. From near its middle a large duct, 

 the sinus superior, extends dorsally, and from the upper end of this sinus pass off 

 the anterior and the posterior semicircular canals. Each canal bends ventrally 

 and after enlarging into an ampulla, connects with an end of the utriculus. 

 Close to the region at which the ampulla of the posterior canal unites with the 

 utriculus, the horizontal canal arises and, after a semicircular course, it enlarges 

 to form an ampulla and then unites with the utriculus near the place where the 

 ampulla of the anterior canal joins that organ. In the utriculus close to its 

 anterior end is a sensory patch, the macula acustica recessus utriculi, over 

 which a small otolith, the lapillus, is found. Each of the three ampulla of the 

 semicircular canals contains a sensory patch, the crista acustica, but these are 

 unprovided with otoliths. No macula neglecta could be found. Unlike the 

 sacculus and the lagena, which are mostly surrounded by bone, the utriculus 

 and the semicircular canals lie for the most part in the loose tissue between the 

 brain and the wall of the skull. The horizontal canal and the posterior vertical 

 canal are in part surrounded by bone, but the anterior vertical canal merely 

 rests against the bone that forms the inner surface of the skull. 



It is thus clear that the ear of the squeteague is not a single sense organ, 

 but two organs structurally distinct — what may be called the saccular organ 

 including the sacculus with its outgrowth, the lagena, and its two sensory 

 patches and two otoliths, and the utricular organ including the utriculus and 

 its three semicircular canals, with four sensory patches and one otolith. 



FUNCTIONS OF THE EAR. 



As was stated at the outset, three chief functions have been ascribed to the 

 vertebrate ear. The sense of hearing has long been associated with the cochlea 

 and adjacent parts of the internal ear, and recent discoveries confirm this view. 

 The bodily equilibrium of vertebrates was shown by Flourens (1828) to be seri- 

 ously interfered with on cutting the semicircular canals, and though there has 

 been opposition to this view, the work of Mach (1874a, 1874b), Breuer (1874), 

 and many recent investigators has added much in support of it. Finally, 

 Ewald (1892) has pointed out, in a most elaborate study, that the internal ear 

 exerts an influence on the tonus of skeletal muscles — i. e., the vigor of an animal's 

 movements is largely dependent upon the integrity of this sense organ. 



