4 CLASSIFICATION OF MONOCARDIAN ANIMALS. 



appearance they then exhibit, few will study, and still 

 fewer will collect them. Hence the ichthyologist has 

 much greater difficulties to contend with, in regard to 

 m-aterials, than he would experience in any other division 

 of the Vertebrata, while he finds himself totally at a loss 

 for that information on their natural habits, " their lives, 

 and their loves," which gives such a charm to the his- 

 tory of other animals, and excites such a popular interest 

 with the generality of readers. But to these difficulties 

 lying in the way of nearly all who write upon ichthyo- 

 logy, must be added others, more particularly applica- 

 ble to our present undertaking. So little has been done 

 towards a natural classification of fishes, more especially, 

 that to attempt those rigorous definitions we have ven- 

 tured upon in the class of birds, would be altogether im- 

 possible. The synthetic mode of investigating our sub- 

 ject is, therefore, that which we shall in many instances 

 adopt. We shall set out, it is true, with the impression 

 that the same general laws which regulate the forms of 

 quadrupeds and birds will be equally apparent in mono- 

 cardian animals. But this belief is not to be received 

 as true, upon trust ; it is not to be unsupported by facts, 

 or to remain as a mere assertion. We shall not, indeed, 

 begin with analysing the smaller groups, and then gra- 

 dually proceed to higher assemblages; for this is the 

 analytical method of investigation — the very reverse of 

 the synthetic : we shall, on the contrary, take a com- 

 prehensive view of those large assemblages, or groups, 

 which nearly all our predecessors have agreed to keep 

 distinct, however they may have diffiired in their sub- 

 ordinate details, or in the series wherein they have 

 placed them. These we shall endeavour to define by their 

 most prominent characteristics, and combine in such a 

 way as that no palpable violation of nature should be 

 committed. We shall then proceed to the results : it 

 will then be seen how far this arrangement is in har- 

 mony with our previous disposition of the other Verte- 

 brata, and how far it is supported by the analogies or 

 resemblances that may be traced between them and the 



