FUNDAMENTAL RELATIONS OF ANIMALS 71 



form similar respiratory functions, and yet they are only modified 

 tracheae which are constructed upon such a peculiar plan and stand 

 in such different relations to the peculiar kind of blood of the 

 Articulata, that no homology can be traced between them and the 

 limgs of Vertebrata, no more than between the so-called lungs of the 

 air-breathing Mollusks, whose aerial respiratory cavity is only a 

 modification of the peculiar kind of gills observed in other Mollusks. 

 Examples might easily be multiplied; I will, however, only allude 

 further to the alimentary canal of Insects and Crustacea, with its 

 glandular appendages, formed in such a different way from that of 

 Vertebrata, or Mollusks, or Radiata, to their legs and wings, etc., 

 etc. I might allude also to what has been called the foot in Mollusks, 

 did it not appear like pretending to suppose that anyone entertains 

 still an idea that such a name implies any similarity between their 

 locomotive apparatus and that of Vertebrata or Articulata; and yet, 

 the very use of such a name misleads the student, and even some of 

 the coryphees of our science have not freed themselves of such and 

 similar extravagant comparisons, especially with reference to the 

 solid parts of the frame of the lower animals. 



The identification of functions and organs was a natural conse- 

 quence of the prevailing ideas respecting the influence physical 

 agents were supposed to have upon organized beings. But as soon as 

 it is understood how different the organs may be which in animals 

 perform the same function, organization is at once brought into such 

 a position to physical agents as makes it utterly impossible to main- 

 tain any genetic connection between them. A fish, a crab, a mussel, 

 living in the same waters, breathing at the same source, should have 

 the same respiratory organs, if the elements in which these animals 

 live had anything to do with shaping their organization. I suppose 

 no one can be so short-sighted, as to assume that the same physical 

 agents acting upon animals of different types must produce in each 

 peculiar organs, and not to perceive that such an assumption implies 

 the very existence of these animals, independently of the physical 

 agents. But this mistake recurs so constantly in discussions upon this 

 and similar topics, that, trivial as it is, it requires to be rebuked.^^ 



*^ I hope the day is not far distant when zoologists and botanists will equally dis- 

 claim having shared in the physical doctrines more or less prevailing now, respecting 

 the origin and existence of organized beings. Should the time come when my present 



