462 CHAKLES S. TOMES. 



favourable specimens fine lines may be seen to run through it 

 more or less at right angles to its surface. 



The ling (Molva) and hake (Merlucius) are the two genera 

 in which the teeth are largest and most conspicuous ; they are 

 also the genera in which the development of the vascular net- 

 work is most complete. In the genus Gadus the arrangement 

 of the vascular canals is somewhat diflFerent, the loops are more 

 rounded^ and the peripheral loops less flattened^ so that there 

 is no appearance of a circumferential vessel such as was seen 

 in the ling and hake, and consequently the outer non-vascular 

 layer of the dentine is less sharply marked off (figs. 5 and 6). 



In the common cod (G. morrhua) the teeth are fairly large 

 and are not very firmly fixed, having a certain degree of motion, 

 though nothing approaching to the very definite hinge (4, 

 p. 224) of Merlucius is to be found. The vascular network is 

 rich, but it takes the form of isolated loops to a great extent 

 (fig. 5) ; the lamination already spoken of exists, but is 

 perhaps rather less marked than in the ling or in the hake, and 

 there is the usual enamel tip to the teeth. The whiting pout 

 (Gadus luscus) has (fig. 6) a similar structure in its teeth, as 

 has also the poor cod (Gadus minutus), although in this latter 

 the canals are less abundant (fig. 7). 



But in the remaining species of the genus Gadus the reduc- 

 tion goes much further; thus the pollack (Gaduspollachinus) 

 has dentine in which the vascular loops remain much more 

 distinct from one another, and there are larger intervals of 

 laminated matrix without any (fig. 8). In the haddock 

 (Gadus seglefinus) the whole upper part of the tooth is 

 often composed of finely laminated dentine without any vas- 

 cular canals, while in the lower portion they do occur as sparse 

 and isolated loops (fig. 9). 



In the whiting (Gadus merlangus) the loops are present 

 in about the same proportion as in the pollack, while in the 

 coal-fish (Gadus virens) they are still more scanty, being 

 confined to a few loops here and there (fig. 10). 



Thus of the whole genus Gadus it may be said that in none 

 do the vascular channels present the beautiful and complete 



