105 



The Food of the Sole, and its Method of Feeding. 



Although the sole is more active by night than by day, it can often be seen feeding 

 in our tanks in the daytime : there is not a constant supply of food in the tanks, and 

 when food is thrown in the fishes are usually so hungry that they begin to feed at 

 once. The food supplied to the soles and other flat-fishes consists principally of marine 

 worms (chiefly Nereis Dumerilii), shrimps, and fish cut up into small pieces, usually 

 pilchard, mackerel, or gurnard. Of these the soles prefer the worms. In seeking their 

 food the soles are guided first of all by the sense of smell : by this they perceive the 

 presence of food in their neighbourhood, and the sense of sight is not employed 

 for this purpose. But in hunting for their food, and in localising its position before 

 biting at it, they rely entirely on the specialised tactile filaments of the skin on the 

 under side of the head. A sole when searching for food moves slowly about gently 

 tapping every part of the sandy bottom with the lower surface of its head. While 

 the sole is thus engaged its back is very frequently covered with a thin layer of 

 sand, so that scarcely any part of it is visible except the eyes and mouth and some 

 of the filaments below the snout when the latter is raised : it is only noticeable on 

 account of its movements, and because its form can be traced out and distinguished 

 from the flat surface of the sand around it. When in the course of this deliberate 

 exploration the lower side of the head feels a worm or other morsel of food, the sole 

 immediately seizes it with a vigorous and sudden snap of the lower half of the jaws 

 where the teeth are situated, and then swallows it with the sand which adheres to it. 

 I have often placed a worm on the upper side of a sole thus engaged in hunting its 

 prey. When this is done it makes not the slightest difference to the sole's behaviour : 

 the fish goes on tapping as before, evidently unconscious that it is carrying a palatable 

 morsel about with it. When the sole feels a worm or other piece of food with its 

 tactile filaments it cannot see it, and it never snaps at any food which it has not first 

 felt in this way. It is in fact unable to localise the position of its food and so to 

 direct the motion of its jaws to the object to be seized unless it has felt this object with 

 these tactile filaments. In other words the afferent sensory impulse produced by the 

 contact of the food with the sensitive filaments is necessary for the co-ordination of the 

 movements of the head and jaws by which the food is seized. 



I have examined the intestines of a large number of soles in order to discover what 

 they had been feeding on before they were caught. It is the custom of trawlers to gut 

 their soles on board before they put them away in the hold of the vessel. They also 

 gut turbot, brill, dorey, and haddock, though of the latter they do not usually catch 

 many off Plymouth ; sometimes they take a considerable number off Mount's Bay and 

 the north coast of Cornwall. I obtained the intestines of soles sometimes by puttino- 

 them into a jar of spirit when I was out with a trawler myself, more frequently by 

 sending jars of spirit on board a boat and paying the men to bring back in them the 



