6 CLASSIFICATION OF MONOCARDIAN ANIMALS. 



to scientific men for placing the different branches of 

 human knowledge before them in the most easy and 

 comprehensible form consistent with sound philosophy; 

 and however highly they may estimate the profundity 

 of those who expatiate on the intricacies of their art^ 

 they will most assuredly follow and admire such writers 

 only as choose an opposite course ; and by the simplicity 

 of their instruction^ and the facility with which their re- 

 searches may be verified, hold out attractions to those who 

 desire to see science disencumbered of all unnecessary 

 mystery^ abstruse technicalities, or empirical assertions. 



(4.) In prosecuting our labours upon these principles, 

 we shall;, in the first place, inquire into the station occu- 

 pied by the monocardian animals in the zoological circle; 

 and then_, taking each of the classes of fish, amphibia, and 

 reptiles^ separately, condense the most remarkable and 

 essential facts relative to their organic structure, both 

 internal and external. Of these three classes^ Ichthyo- 

 logy, or that which treats of fishes, "^vill claim our first 

 and chief attention, not only as being by far the most 

 numerous and interesting, but also because it is that 

 with which we are most conversant. Ichthyology, in 

 fact, engaged our attention long before ornithology; and 

 no opportunity has been lost, during a period of twenty- 

 three years, of making drawings and descriptions from 

 living specimens in all those foreign countries we have 

 visited. Many years' residence in Sicily and other parts 

 of the Mediterranean will enable us to give much inform- 

 ation, hitherto unpublished, on the rarer fishes of 

 those coasts, sufficient, at least, to show how imperfectly 

 they have as yet been made known. Our information on 

 the reptiles and Amphibia is more confined; but as the 

 determination of the natural groups, and not the species, 

 is our chief object, this circumstance becomes of less 

 consequence. In this we have derived much assistance 

 from the labours of our friends MM. Gray and Bell, 

 as well as from the numerous and valuable continental 

 works published of late years on these animals. 



(5.) Fishes, along with frogs and reptiles, constitute 



