of certain littoral Mollusca. 389 



inconclusiveness of those experiments for proving the respiratory organs 

 of Melampus, Pedipes, &c. to be pectinated, by showing that the 

 animals of Limiuea, with respiratory organs well known not to be so, 

 are equally capable of supporting life under similar circumstances, it 

 will establish at least the fact, that a class of animals exists, which, 

 with respiratory organs originally formed for breathing atmospherick 

 air, have yet the power either of accommodating these very same 

 organs, (not of developing or employing different ones, as certain Rep- 

 tilia do in the converse case*), to the abstraction of oxygen from 

 water, or also, perhaps, even of supporting life solely by the action of 

 the water on the integuments or mantle : by, in short, a sort of conver- 

 sion of the whole exposed surface of the body into a breathing apparatus, 

 without employing the aerial breathing organs at all. It must indeed be 

 admitted, that in animals like these, in which the influence of oxygen 

 on the blood is tending fast to its minimum, it is not difficult to imagine 

 that the system of the animal functions may with much greater theo- 

 retical plausibility be conceived capable of accommodating itself to such 

 a change, than in higher races of animals and types of organization : in 

 w^hich the oxygenous fluid exercises a much more powerful influence, 

 and plays a far more important part in the conditions of vitality. 



The solution of this problem is equally interesting in a geological 

 point of view as in others. It will tend to demonstrate the right or wrong 

 collocation of many fossil shells; a question of so much consequence in 

 the discrimination of various strata. It will go to prove whether certain 

 genera which have been heretofore referred to the land or fresh-water 

 Pulmonifera do or do not belong to the marine or at least littoral Pecti- 

 nibranchiata. I am therefore proportionately interested in its right 

 determination ; and no farther anxious for the verification of my former 

 inferences, than as far as regards the establishment of the truth. They 

 will stand, at all events, as useful starting points for the researches of 

 others : and the conclusions there drawn (some of them certainly too 

 positively) will also, if proved erroneous, serve to display the necessity of 

 extreme caution in all inductive reasoning to Naturalists in general. 



* See Note f, page 387, 



