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with ? Is it possible to recognize anything like a unity 

 of type amongst creatures so differently constructed, 

 and so widely removed from each other in their habits, 

 aspects, functions, and attributes? Such questions as 

 these, however, though they may occasionally perplex 

 the tyro, or amateur, are not likely to be raised by any- 

 one who has mastered the merest alphabet of zoology, 

 and who is aware that the integrity of Nature is some- 

 thing real and positive, as experience indeed is ever 

 tending more and more to corroborate, and by no means 

 the day-dream of an enthusiastic, or fertile, imagination. 

 To trace out the progressive development of animal life, 

 from its humblest phases ; and to mark, as they become 

 visible in the intermediate grades, the first rudiments 

 of organs and instincts which are destined to attain 

 their maximum in the higher ones, embody but a small 

 portion of what it is the naturalist's mission to investi- 

 gate. To him belongs the special privilege of inquiring 

 dogmatically into this structural advancement ; and of 

 suggesting methods of classification which shall accord, 

 in their several component divisions, so far at least as is 

 practicable, with the constitutional change. We should 

 recollect, however, that this system, being based upon 

 truth, must, if it would be consonant throughout, adapt 

 itself to all the various phenomena (in their respective 

 positions, in the scale), from the consideration of which 

 it should be exclusively deduced, or built. To draw 

 broad conclusions of any kind, or to attempt the esta- 

 blishment of propositions and principles, from simple 



