STRUCTUKE OF LAMPREY. 121 



devoid of both pectoral and ventral fins. A long 

 fleshy fold of the skin runs round the hinder end of the 

 body, but having no true rays it can hardly be called a 

 fin. The skeleton is entirely cartilaginous ; there are 

 no ribs or other appendages, and the skull is quite rudi- 

 mentary. The mouth is a singular affair, not unlike 

 the large end of a fimnel, dotted all over with small 

 hook-like teeth. Any living thing caught in this for- 

 midable trap would stand but a sorry chance of ever 

 getting out again. The breathing apparatus is ex- 

 tremely curious, and wonderfully adapted to fulfil the 

 purposes for which it is intended. Instead of gills, as 

 in ordinary fishes, the breathing organs in lampreys 

 are in the shape of tiny sacs, the inner surfaces of 

 which are thickly covered with a perfect network of 

 blood-vessels. There are seven of these sacs on each 

 side of the fish's body placed near the head, and each 

 sac communicates externally with the water by a 

 separate orifice. In describing these curious breathing- 

 holes, Professor Owen says : ' When the lamprey is 

 firmly attached, as is commonly the case, to foreign 

 bodies by means of its suctorial mouth, it is obvious 

 that no water can pass by that aperture from the 

 pharynx to the gills ; it is therefore alternately re- 

 ceived and expelled by the external aperture.' The 

 water, besides gaining admission by these seven canals 

 to the bronchial sacs, is let in by the mouth, if the 

 animal so wills it, or by a round hole observable on the 

 top of the head. This aperture has a direct communica- 

 tion with the pharnyx. The habit of the lamprey is to 

 fasten itself firmly to large stones or rocks by its sucker- 

 like mouth, and it is said by some writers that they like- 

 wise fix themselves on to the bodies of other fish, and 

 devom^ them whilst they are alive. This statement we 



