240 



ZOOLOGY 



SECT. 



matter, which passes with little or no alteration through its enteric 



canal. Its movements are for the 

 most part very sluggish, and are 

 chiefly effected by the agency of the 

 tail-fin. .The paired fins are employed 

 in steering and balancing and in the 

 ascending and descending movements : 

 owing to their great flexibility they 

 are entirely incapable of supporting 

 the body when the fish is removed 

 from the water, but the pectoral fins 

 2 may be employed as props when it 

 | lies in a resting condition at the 

 | bottom. 



External Characters. The body 

 ? is fish-like (Fig. 914) with a diphycercal 

 g caudal fin. The surface is covered 

 Q with thin, bony, imbricated cycloid 

 | scales, very large on the head and 

 trunk, somewhat smaller towards the 

 . tail end, and very much smaller over 

 | the fins and the posterior part of the 

 I operculum. 



The limbs have a characteristic 

 shape, being in the form of two pairs 

 of elongated, leaf -like, pointed paddles. 

 The marginal parts of the paired fins 

 and the whole extent of the unpaired 

 or caudal fin are supported by a double 

 series of slender fibre-like un jointed, 

 partly ossified, dermal rays (campto- 

 trichia), which are much more numer- 

 ous than the endoskeletal rays and 

 which are covered by small surface- 

 scales. 



The mouth is situated on the ven- 

 tral surface of the head, close to the 

 anterior extremity of the snout. The 

 external nares differ from those of 

 other Vertebrates in being situated 

 immediately outside the aperture of 

 the mouth, enclosed within the upper 

 lip. A pair of internal nares opens 

 not far behind them into the anterior 

 part of the mouth-cavity. At the 

 root of the tail is the cloacal aperture with an abdominal pore on 

 either side of it. There is an operculum similar to that of the 



