OF CREATION. 151 



structure of these spines, as seen under the micros- 

 cope, is hardly to be distinguished from that of teeth ; 

 and in this way, an almost anomalous contrivance, 

 introduced, doubtless, for a special purpose, is found 

 to resemble a totally different organ, adapted for pur- 

 poses altogether distinct and peculiar. The spines 

 may also have served as defensive weapons, but are 

 not likely to have anything to do with ordinary loco- 

 motion. They produce a sudden and considerable 

 impulse corresponding to the great muscular energy 

 of these creatures, and prevent the delay that would 

 necessarily arise if the animal had to check its motion 

 through the water while pursuing and when in the 

 act of capturing its prey. Spines on the backs of 

 sharks are not confined to one genus, but seem to 

 have been common appendages to the dorsal fins of 

 most of the ancient species. Being hard, indestruc- 

 tible, and readily detached after death, they have 

 often been preserved in a fossil state ; and from their 

 variable markings, deep furrows, and hooked teeth, 

 we are able to determine a large number of species of 

 these long extinct animals. Unfortunately, since the 

 teeth almost the only other hard part of sharks 

 are not found directly associated with the spines, we 

 may probably often describe and name the same 

 species twice over, especially when the specimens 

 are from the same strata, since we are not in a 

 condition to determine the relation that may have 

 existed between the two kinds of organic remains. 

 The sharks of the lias attained a large size, and 

 were exceedingly abundant and voracious. 



The other fishes of the lias, most remarkable for 

 their number or peculiarity of form, are of much 



