VERTEBRATE ZOOLOGY. 461 



"The author lays no stress on the characters formerly 

 given as distinctive of osteo-dentine i. e., (1) a laminated ar- 

 rangement of the matrix is not unknown in vaso-dentine; (2) 

 lacuna} are very frequently absent from bone in fishes, and 

 very frequently from osteo-dentine, so that these characters, 

 as those who have tried to apply them have found, are not 

 useful in practice." 



Mr. Tomes has also been struck by the peculiarity of the 

 teeth of the hake (Merlucius) and some other fishes. "The 

 attachment of the teeth of the hake is so peculiar as to merit 

 a word of notice. The inner and longer of the two rows of 

 teeth are set upon elastic hinges, which allow of their being- 

 bent inward towards the throat, but cause them at once to 

 spring back into the upright position when pressure is taken 

 off them. This arrangement, shared by the angler, was hard- 

 ly to be expected in one of the Gadidae; but the author has 

 found in others of the family steps towards this highly spe- 

 cialized arrangement, the benefits of which, to a voracious 

 predatory fish, such as the hake, are obvious. 



" The common cod has teeth which admit of a small amount 

 of motion only ; but a comparison of them with those of the 

 hake shows clearly that a further modification in the same 

 direction would lead to an attachment similar to that of the 

 latter fish. 



"The haddock, which in this respect is a fair represen- 

 tative of the family, has teeth which admit of no motion at 

 all." 



This depressibility and mobility of the teeth is, however, 

 by no means as uncommon as Mr. Tomes has evidently sup- 

 posed. It seems to be characteristic of those fishes in which 

 the teeth increase in size in the inward rows. It was long 

 ago (in 1802) shown to be the case in the hake by Gill, and 

 it also occurs not only in the Lophiids and Esocids, but in 

 the Ceratiids, and many Serranids, Blenniids, Gobiids, and 

 others. Even in the case of some fishes with obtuse arma- 

 ture, the teeth are movable; this is notably the case in Pleu- 

 ronectes, one of the flatfishes, the teeth of which may almost 

 be played upon like the keys of a piano, during the breeding 

 season, though at other times quite fixed. 



