CYCLOSTOMES. 21 



points reflected backwards. They are usually described as distinct 

 teeth, and, viewed as such, form two concentric curved lines inter- 

 rupted at the middle of the tongue. In the Myxine glutinosa the 

 number of lingual teeth is gig, i. e., there are eight teeth in both the 

 right and left anterior rows, while there are eight in the left posterior 

 row, and nine in the right posterior row. In the Bdellostoma hep- 

 tatrema, there are fzj lingual teeth ; in Bdell. heterotrema, the number 

 is }iZi2 ; in the Bdell. hexatrema, the lateral rows of lingual teeth are 

 symmetrical, being \\z\\ ; in Bdell. cirratum, there are }t-ii teeth ; 

 in Bdell. dombeyi, the number is ^yZ^;. These formulae appear to be 

 constant in the species ; this is, at least, the case in the glutinous 

 hag. The middle teeth are always the longest, the rest gradually 

 diminish towards 4:he lateral extremities of the rows.(l) 



I have already alluded to the parasitic habits of these low 

 organized fishes. When they first attach themselves to their prey, 

 the single median recurved palatal tooth is thrust into its flesh, and 

 serves as a holdfast, while the work of destruction is carried on by 

 the laterally opposed lingual saws, aided by the suctorious action 

 of the mouth. The usual situation in which the myxine is found, 

 is the interior of a cod or other large fish, into whose carcase it has 

 thus penetrated, and on whose soft parts it has preyed. 



LAMPREYS. 



11. In the lampreys fPetromyzonJ ,(2) there are labial and inferior 

 maxillary, as well as palatal and lingual teeth ; all these are likewise 

 horny substances, of a simple, conical, sharp-pointed, form, and of a 

 somewhat less dense texture than in the myxinoids. They are 

 hollow, and supported on conical, reproductive pulps. The pulps 

 of the labial teeth are firmly attached by their base to the fibrous 

 tissue of the lining membrane of the lip. 



The labial teeth of the outer or marginal circle are the smallest ; 

 from these, the teeth increase in size as they approach the centre of 

 the cavity of the mouth. The converging series in the mesial plane 

 are arranged in a straight line ; those of the sides in curved lines, 

 with the concavity towards the lower margin of the mouth. In the 



(1) See Miiller, ilber den Myxinoiden, p. 20. (2) PI. 2, figs. 4 and 5. 



