466 CHARLES S. TOMES. 



animals, and the question next presents itself, what lines do 

 they follow ? 



The first thing that would suggest itself is that as the denti- 

 tions become less pronounced, and the individual teeth smaller, 

 so does their intimate structure become simplified. 



Some facts may be adduced in support of this view ; thus 

 the most elaborate tooth structure is found in the two genera 

 which have the largest teeth, namely, the hake and the ling 

 (figs. 1 and 2); while in the Lota (fig. 11), which is regarded as 

 allied to the ling, the teeth are both much smaller and simplified 

 in structure. Similarly, Gadus minutus, which has teeth 

 large for the size of the fish, has a richer vascular network than 

 many of the genus possess. But if this be a truth, it is only 

 a partial truth, for, at all events in the same individual, the 

 size of the tooth does not determine its structure. 



For the hake is peculiar in having comparatively long and 

 moveable gill-rakers upon its first gill arch, and these gill 

 rakers are beset with tiny teeth ; nevertheless these minute 

 teeth are exactly, so far as space will allow, of the pattern of 

 the large teeth which are twenty times their size, so that here 

 at least reduction in size has not been accompanied by any 

 simplification of structure (fig. 2"^). Again Uraleptus (fig. 13) 

 has teeth of quite considerable size, but they are almost devoid 

 of vascularity, while teeth from its branchial arches exactly 

 agree in structure with its large teeth (fig. 14). 



A similar inference may be drawn from the teeth of the 

 Cha3todonts (4, p. 249) in which the teeth, although attenu- 

 ated to an extreme degree, yet retain a full supply of 

 vascular canals whenever there is room for them. Hence 

 there seems to be some degree of fixity in the vascular pattern 

 of dentine, and it does not seem to be quite lightly abandoned, 

 as might at first be inferred from the fact that within the 

 single genus Gadus so many grades of vascularity are met with. 

 It seems possible that the fact that a large tooth like that of 

 Uraleptus should present that absence of vascularity which 

 pertains to the reduced dentitions, might be accounted for by 

 the supposition that the ancestors of this genus had suffered 



