IDENTICAL TYPES FOUND EVERYWHERE. 21 



extensively studied in their direct reference to the world 

 iii which animals live. If this had been done, we should 

 no longer call by the same common name of legs and 

 wings, organs so different as the locomotive appendages 

 of insects and those of birds ! We should no longer call 

 the breathing cavities of snails lungs, as well as the air- 

 pipes of mammalia, birds and reptiles ! A great reform 

 is indeed needed in this part of our science ; and no 

 study can better prepare us for it than the investigation 

 of the mutual dependence of the structure of animals and 

 of the conditions in which they live. 



SECTION III. 



REPETITION OF IDENTICAL TYPES UNDER THE MOST 

 DIVERSIFIED CIRCUMSTANCES. 



As much as the diversity of animals and plants living 

 under identical physical conditions shows the independ- 

 ence of organized beings of the medium in which they 

 dwell, so far as their origin is concerned, so independent 

 do they appear again of the same influences when we 

 consider the fact that identical types occur everywhere 

 upon earth under the most diversified circumstances. If 

 we sum up all these various influences and conditions of 

 existence under the common appellation of cosmic influ- 

 ences, or of physical causes, or of climate in the widest 

 sense of the word, and then look around us for the ex- 

 treme differences in that respect upon the whole surface 

 of the globe, we find still the most similar, nay, identical 

 types, (and I allude here, under the expression of type, to 

 the most diversified acceptations of the word,) living nor- 

 mally under then- action. There is no structural differ- 

 ence between the herrings of the Arctic and those of 



