462 THE BIOLOGY OF MARINE ANIMALS 



No clear-cut picture emerges from correlated studies of behaviour and 

 physiology of the teleost brain. In some teleosts decerebration and re- 

 moval of the habenular ganglion failed to abolish learning or impair 

 visual form-discrimination (Gasterosteus, Phoxinus, Gobio). In other species, 

 however, forebrain injuries produced marked disturbances of behaviour, 

 affecting mating, schooling, etc. {Carassius, Box, etc.). The function of the 

 forebrain in teleost behaviour appears to be a highly variable one, closely 

 linked with the importance of the various sensory avenues in any given 

 species. Thus, olfaction is the dominant sensory modality in some species; 

 tactile or visual sensations in others. Among the latter should be included 

 those species with highly developed visually directed activities such as 

 breeding behaviour and schooling. Further experiments have shown that 

 the optic tectum contains a mechanism involved in second-order learning. 

 The forebrain thus possesses affector and associative centres for certain 

 aspects of behaviour, and these are linked with association centres at lower 

 levels (72, 95). 



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