150 CLASSIFICATION OF FISHES. 



We have illustrated this position so fully in the two most 

 perfect classes of vertebrated aniraals_, and more especially 

 among birds, that it appears hardly necessary to touch 

 upon the subject in this place ; but as this volume wiU, 

 doubtless, be perused by many ichthyologists who have 

 not turned their attention to ornithology, it seems ne 

 cessary to explain to them the leading principle upon 

 which we universally proceed in analogical comparisons, 

 and upon which the essence of our theory depends. True 

 it is, that there are sharks wdth spined dorsal fins ; and 

 this fact would appear to invahdate the character we have 

 given to the family ; but it w^ill be seen that these spined 

 sharks are not the most typical, and therefore they are 

 not taken into the account at present : the same may be 

 said of such as, from being covered with spinas, are 

 analogous to the sturgeons and the cheloniform fishes. 

 In explanation of all which w^ e may observe, that these 

 minor variations, belonging only to aberrant forms, are 

 to be explained by this simple law of nature,— that every 

 circular group, whether large or small, contains within 

 itself representations of all other groups ; so that if, 

 among the sharks, there were none with spined rays, 

 there would be no representation of the order Acanthop- 

 teryges, and (unless other analogies to that order existed) 

 the sharks would be an imperfect circle. We hope the 

 experienced zoologist, to whom all this is well known, 

 will excuse our again explaining these views to the ge- 

 neral student, and we shall now proceed to the compari- 

 son above intimated. 



(132.) The most typical forms of the rays, as will 

 subsequently appear, are those whose backs are pro- 

 vided with a formidable spine, usually, although im- 

 properly, denominated a sting. This weapon is placed, 

 indeed, upon the tail, generally near its base ; but so also 

 is the first dorsal fin in several types of the sharks ; so 

 that it becomes no more nor less than are presentation 

 of the first or spinous dorsal fin of acanthopterygious 

 fishes. It may be here observed, that some of the rays 

 have two spines, analogous to the two dorsal fins of 



