^ae MANUAL OF ZOOLOGY. 



when present it does .not communicate with the oesophagus by 

 a duct. 



As in the preceding order, the Anacanthini are divided into 

 two groups, distinguished by the presence or absence of the 

 ventral fins. In the first of these groups {Apoda) are only a 

 few fishes, of which one of the most familiar examples is the 

 little Sand-eel {Ammodytes lanced), which occurs on all our 

 coasts. In the second group {Sub-brachiatd) in which ji^entral 

 fins exist, are the two important families of the Gadida and 

 PleuronectidcR. The Gadidce or Cod family, comprising the 

 Haddock, Whiting, Ling, and Cod itself, is of great value to 

 man, most of its members being largely consumed as food. In 

 the PleuronectidcR or Flat-fishes are comprised the Sole, Plaice, 

 Turbot, Halibut, Brill, and others, in all of which th^re is a 

 very curious modification in the form of the body. The body, 

 namely, in all the Flat-fishes (fig. 144) is very much compressed 



Fig. 144. — Pleuronectida. R/iombus ptinciaUfs, Natural size (after Gossc). 



from side to side, and is bordered by long dorsal and anal fins. 

 The bones of the head are twisted in such a manner that the 

 two eyes are both brought to one side of the body, which is 

 sometimes the right side, sometimes the left. The fish usually 

 keeps this side uppermost, and is dark-coloured on this aspect;; 

 whilst the opposite side, on which it rests, is white. From this 

 habit of the Flat-fishes of resting upon one flat surface, the 

 sides are often looked upon as the dorsal and ventral surfaces 

 of the body. This, however, is erroneous, as they are shown 

 by the position of the paired fins to be truly the lateral surfaces 

 of the body. The mouth has its two sides unequal, the pec- 

 torals are rarely of the same size, the ventrals look Uke a con- 

 tinuation of the anal fin, and the branthiostegal rays are six in 

 number. 



