610 



DR. BASHFORD DEAN ON 



movements of the gills varied from twenty-two to thirty-one 

 a minute. Both fish had long been quiet ; if their movements 

 had been active there is no doubt that this rate would have been 

 notably exceeded. 



Rhythmic movements in breathing are well shown in the 

 opercular membrane. In the early stage of breathing the cheek 

 in the subopercular region is seen to dilate slowly and strongly ; 

 this dilated region is then passed (rather slowly) backward, and 



Text-fig. 84. 



"r'-'^mj^ 



Opercular movement in breathing of Ceratodus Jhrsteri. 

 The crest of the nndulatory wave is indicated by the asterisk. 



its enclosed water is discharged (text-fig. 84). During this 

 process the dilated part becomes more and more conspicuous 

 until the final discharge, and at that moment the free rim of the 

 gill-opening is thrown outward and drawn forward, exposing the 

 lighter coloured hinder border of the gill-slit. The free border up 

 to that time has been closely apposed to the head. 



It was earlier noted that Ceratodus is a " nostril breather." 



