No. 435-] SEXSE OF HE A RIXG IX FISHES. 199 



The lateral-line organs can also be shown to possess a stimulus 

 peculiar to themselves. These organs were originally supposed 

 to be merely slime glands for the production of the slimy cover- 

 ing so characteristic of the skins of fishes. In ICS50 Leydig 

 demonstratcd their sensory character, and since then they have 

 given rise to much speculation among naturalists. Since they 

 occur in fishes that have the usual five senses, Leydig (1868) 

 regarded them as organs of a sixth sense quite distinct from any 

 that we possess. Schulze ( 1870) thought they served to detect 



surface of a fish or the fish swims through the water. Merkel 



Emery (1880) and V. and F. Sarasin (1887-1890) regarded 

 them as accessory ears. Fuchs (1895) brought forward evi- 

 dence to show that they were pressure organs, and Richard 

 (1896) believed they were in some manner connected with the 



(1896) was of opinion that among other things they oriented the 

 fish in reference to centres of disturbance in the water, and Lee 

 (1898) thought them organs of equilibration. Thus, much dif- 



In the killifish the stimulus for the lateral-line organs is easih 



to undergo a slight inaudible oscillation by some means not visi- 

 ble to the fish, the latter will dart at once to the bottom. _ This 

 happens even when the oscillation is scarcely perceptible to the 

 observer. After the nerves to the lateral-line organs have been 



rgans have been 



