66 



BRAIN AND BODY OF FISH 



We have drawn attention already to this unfortunate terminology 

 " valvular It is a valve only in the sense that it separates the two 

 halves of the tecta optica, and it does so particularly in those fish 

 that grub in the mud and search between stones, such as the barbel 

 and gudgeon among the Cyprinoids. The valvula is thus a forward 

 tongue starting from the anterior aspect of the base of the cerebellum. 

 It is this that has burgeoned forth, one might almost say, bubbled 

 over so as to make a thick cap that covers the whole brain just as the 

 cerebral hemispheres do in the human brain. 



\lalvulii 





Xx.. 





/<f1^.CU:.t^S/'''Co 



Fig. ix.^ — Section of brain of Mormyrus. — Semi-diagrammatic to show 

 cerebellum acoustic and lateralis lobes enveloped by valvula cerebelli. 



To make this description clear we reproduce a sketch (Fig. viii), 

 redrawn from R. H. Burne ; this has been also figured by Herrick, 

 who does not agree with the identification of the two ovoid masses 

 that form the medulla as the " lobus impar " as shown in Burne's 

 lettering. I have had the opportunity through the kindness of 

 Dr. Tate Regan, and more recently Dr. Norman, of examining three 

 species of Mormyrida?, and have examined them both by the naked 

 eye and by serial sections. After making a number of serial di'awings 

 and studying the literature of the microscopic structiu-e of the 

 medulla and cerbellum, I have become convinced that the so-called 

 lobus impar consists of a central acoustic area and the acustico 

 lateral lobe. I shall show two drawings of my sections across these 

 lobes, and it will be seen that the eighth nerve j)asses to the central 

 acoustic lobe and that more anteriorly the lateralis nerve enters the 



