SENSES KEPROD UCTION. 523 



Senses, &c. 



Fishes do not seem to have much sense of taste or of 

 smell, but diffuse sensitiveness to touch, chemical stimuli, 

 &c., is well developed, especially on the head and along the 

 lateral line. Though there is no drum, and the ear is 

 deeply buried, they certainly hear; thus there are well known 

 cases of tame fishes coming to the sound of a bell or voice. 

 Experiments have led some to believe that the semicircular 

 canals of the fish's ear are indispensable in the direction 

 or equilibration of movement, and it is obvious that this 

 function is more important to a fish than the luxury of 

 listening. But the results of experiment are still somewhat 

 discordant. The sense of sight is, on the whole, well 

 developed. As to the intellectual powers of their small 

 brains we know little, but many show quickness in perceiving 

 friends or foes, and many of their instincts are complex. 

 At the breeding season there is sometimes an elaborate 

 expression of excitement, well seen in the stickleback. 



Reproduction. 



The sexes are separate, except in Chrysophrys and 

 SerranuS) two hermaphrodite bony fishes, or when abnor- 

 mal hermaphroditism occurs, as in herring, cod, mackerel. 

 In many cases the males are smaller, brighter, and less 

 numerous than the females. Courtship is illustrated by the 

 sticklebacks {Gasterosteus, &c.), the paradise fish (Macro- 

 podus\ and others, and the bent lower jaw of the male 

 salmon reminds us that some male fishes fight with their 

 rivals. 



Most Fishes lay eggs which are fertilised and develop out- 

 side of the body. They may be extruded on gravelly ground, 

 or sown broadcast in the water. Sturgeon, salmon, and 

 some others ascend rivers for spawning purposes, while the 

 eels descend to the sea. In the case of trout, Barfurth has 

 observed that the absence of suitable spawning ground may 

 cause the fish to retain its ova. This results in ovarian 

 disease, and in an inferior brood next season, a fact which 

 should be compared with what Hertwig has observed in 

 regard to Echinoderms, that ova which are retained beyond 

 the normal period become over ripe and pathological. 



