96 BRAIN AND BODY OF FISH 



fish that feed on Crustacea and shell-fish it is well-developed ; but 

 in those fish of predatory habits these lobes are less well marked, 

 but on the other hand the somatic-sensory lobes, or fifth lobes, are 

 highly developed, and in some cases almost envelope the gustatory 

 lobes. 



Plate 18 gives drawings of the dorsal aspect of the species of 

 gadoids, all common and familiar fishes in British waters, except 

 the forkbeards and the deep sea ling, Molva Elongata. 



In the first figure a, which represents the dorsal aspect of the 

 brain of the haddock or " shell-fish," as the Germans call it, the 

 somatic-sensory lobe is of moderate size, but the facial oi gusta- 

 tory lobe, v.f.L, is large. The haddock is the type of a ground 

 feeding gadoid with a diet of Crustacea, molluscs, echinoderms and 

 worms. If we now compare this drawing with Fig. d, which repre- 

 sents the brain of the pollack, a typical predatory fish, the somatic- 

 sensory lobes are very prominent and spread backwards on either 

 side so as to embrace the minute facial lobes which are com- 

 jjletely surrounded by the tapering ends of the lobes which meet 

 posteriorly in the middle line. The pollack is very predacious and 

 its diet is fish and rarely anything else, when fully grown. Between 

 these extremes we have the cod, whiting, and ling, and the size of 

 the anterior (SS) somatic-sensory areas increases according to the 

 importance of fish in their diet, and at the same time the size of the 

 facial or gustatory lobes diminishes as the crustacean and shell- 

 fish element in their diet figures to a less extent ; so that we get 

 a, series, starting from the haddock, of the cod, feeding on Crustacea 

 mollusca and fish ; the whiting, feeding on shrimps but mostly fish, 

 and the ling, feeding almost entirely on fish. The hake has been 

 purposely left out of the series ; the reason for this omission will be 

 clear from the drawing ; the brain pattern is most " uncodlike." 



The cerebellum of the hake is not tongue-shaped as in the 

 gadidse, but is sessile, and is prolonged laterally into the two 

 large acoustic tubercles, from which lateral eminences extend 

 backwards as narrow ridges which meet medially and enclose a 

 tiny lobe, presumably representing the gustatory lobe. We gather 

 from this description that the hake has no business to be included 

 in the gadidse, but should be placed in a separate family, the 

 merluciidae, as recent writers have already done. As both the life 

 history of this fish and its brain pattern are unique we propose to 

 discuss the many interesting facts that arise in a separate chapter. 

 But there are two other features in the gadidse which are of im- 

 portance, the presence or absence of barbels and the relative size 

 of the optic lobes. 



