60 THE ZOOLOGIST. 



With the exceptions noted as from the Indian Ocean or the 

 Mediterranean, all the other fishes of the list are to be found in 

 British waters. 



There are sixteen families represented. As a rule the sagittce 

 in a fish are homogeneous in texture ;* it is more often not so 

 with the asterisci, and this may when they are large enough be 

 noticed with the naked eye. In most of those mentioned above 

 and shown in the plate there is a chalky-looking kind of deposit 

 in the centre of them ; it is most particularly observable in 

 No. 20 (the Tench) and No. 21 (the Carp), owing to the larger 

 size of these asterisci. No. 22 (the fresh-water Bream), however, 

 also one of the Cyprinidce, has homogeneous asterisci. The 

 normal appearance of an asteriscus is of a vitreous description ; 

 this is particularly observable in No. 16 (the Hake), which looks 

 like a delicate piece of Venetian glass. Fifteen out of the twenty- 

 five figured show traces, generally very marked, of this chalky- 

 looking matter in their structure, this being in the centre of the 

 asterisci, whilst the edges keep their vitreous character. This 

 chalky appearance is possibly due to an excess of organic matter, 

 and is not constant ; sometimes the asteriscus of one side shows 

 it strongly, whilst the other side keeps its vitreous character ; in 

 other cases both stones are affected, but in different degrees. 

 The position of the asteriscus in the head, beyond being in the 

 lagena, is difficult to determine on account of their small size, 

 but if the plate is turned upside down the asterisci of No. 21 

 (Cyprinus carpio) will assume the position in which they are in 

 the skull. The then left-hand one showing the inner aspect of 

 this otolith, and the other the outer aspect. 



Why the asteriscus in the Carp family (the Cyprinidce) 

 should have developed so largely and the sagitta dropped into 

 a small rod-like stone is hard to explain. The Pike {Esox lucius) 

 and the Perch (Perca fluviatilis) have the usually developed 

 sagitta, so it cannot be simply that the Carps live in fresh 



* After dissecting for otoliths the skulls of some three hundred different 

 species of fish, with of course often many of the same kind in each family, 

 only three cases of abnormal sagittce have been come across, and these in 

 eighty species of fish from northern waters. The other two hundred and 

 twenty species from the Indian Seas off Madras and the Mediterranean did 

 not produce a single abnormal sagitta. 



