COMPABISONS OF OTOLITHS. 



297 



cretions peculiar to the Scicenidce. A typical example of the 

 remarkable constancy in the same family of fishes of the charac- 

 teristics of the otoliths. 



Fresh-water fishes, as represented by the Perch and the 

 Carp family, are all supplied with fairly large otoliths. The only 

 deep fresh-water fish obtained was the Lota vulgaris, a fresh- 

 water Gadoid fish ; its otoliths, however, for its family, were 

 moderate in size. 



A relation has been sought by comparing the power of vision 

 of a fish as deduced from the muscles attached to the eyeball with 

 their power of hearing, as deduced from the size of the otolith 

 resident in the organs of hearing. In many fishes the recti 

 muscles of the eyeball are attached to the skull at the back of 

 the eye, giving a short range of movement ; this is seen in the 

 Gadida. In others, again, these muscles are long, and go 

 well back from the eyeball, resting in a long, narrow case parallel 

 to the basisphenoid, and divided from the brain-pan by a bony 

 septum ; this is seen in Pagrus auratus, Pelamys sarda, and 

 many others. Observations were made on sixty-seven different 

 species of fishes representing twenty-nine families, and by classi- 

 fying them we get — 



Size of Otoliths. 



Large. 



Small. 



Moderate. 



Those having a long flexible muscle . . . 

 ,, ,, short, strong ,, 

 ,, ,, moderately strong 



muscle to the eye 



12 

 15 



4 



20 

 4 



3 



6 

 3 



The long recti muscles give a quickly mobile eye, and are 

 seen in the Scombrida, which have typically small otoliths. 

 The short, strong muscles are seen in the Gadidce, which have 

 large otoliths. Amongst the sixty-seven fishes above alluded to, 

 the number of those having long rectus muscles giving a mobile 

 eye and that have a small otolith exceeds those having a large 

 otolith by nearly two to one, but in those that have short, 

 strong muscles the number having large otoliths exceeds that of 

 those having small otoliths by nearly four to one. But that 

 quickness of sight makes up for dullness of hearing, or that 

 Zool. 4th ser. vol. XIV., August, 1910. 2 A 



