xlvi. PRESIDENT'S ADDRESS. 



the power of retraction or protraction as well as of opening and 

 shutting. 



The admirable adjustment of the jaw-apparatus compensates 

 for the absence of hands and arms. The whole organisation of 

 a fish is adapted for the element in which it lives and moves. 

 The viscera are packed into a small compass, and repose in a 

 cavity brought forward close to the head ; the consequent 

 obliteration of the neck more firmly connects the head to the 

 trunk. The sharks, whose form of body, and strength of tail, 

 enable them to swim near the surface, are further adapted for 

 an active life, the absence of an air-bladder being compensated 

 for by the large proportional size and strength of their pectoral- 

 fins for raising the body and preventing a rolling movement. 

 In long-bodied and small-headed fish the ventral-fin is placed 

 far back towards the tail, and acts as a balancer. In large- 

 headed fishes the ventral-fin is placed forward to assist the 

 pectoral-fin to raise the head, which with most fish is dispro- 

 portionally large ; this is necessary for rapid progression. 



None of the extinct fish of the Silurian and Devonian Ages 

 have vertebral-centra ; some Ganoids, however, show the con- 

 version of the notochordal capsule into distinct bony segments. 

 The Lepidosiren of the present day retains this notochordal 

 condition, but without the compensating Ganoid scales. On 

 the other hand the Silurida, Cat-fish, combine the tuberculated 

 bony-dorsal-plates or scutes with a well-ossified internal skeleton. 

 The back-bone of the Teleostei consists of separate well-ossified 

 vertebrae ; they constitute the bulk of the fish from the Tertiary 

 Age to the present time. The skull retains much of the primitive 

 cartilage as in the case of the Salmon and the Pike. It is in the 

 abdominal fresh-water fish generally, that the semi-osseous 

 condition of the skull is present. There is generally a renewal 

 of the teeth during the whole of a fish's life, to which there are 

 exceptions. 



Before proceeding to a general survey of the characteristic 

 structure of fish it will be desirable to bestow some attention to 

 the Amphioxtts or Lancelot, which seems to connect the 



