354 RESPIRATION. 



Thus these two distinct sets of processes, by which 

 this important and essential function of animal life is 

 performed, have a distinct set of organs for each, 

 adapted admirably for that, but not for the other. 

 There is no instance of an organization that can 

 perform both operations, though the frequency with 

 which the performance is necessary varies very much, 

 according to the habits of the animal, and the place 

 and manner in which it finds its food. It has been 

 said that there is a change in some cases, from the one 

 of these organizations to the other, in those animals 

 which spend their infant states in the water, and their 

 mature ones alternately in the water and the air, or 

 wholly in the latter ; that the gills, with which they are 

 furnished in the first state, change to lungs when they 

 assume the last. The fact has not been verified by 

 the actual observation of one of those animals at every 

 instant, from the time of its being deposited in the 

 water as an egg, to that of putting on the form and 

 habits in which pulmonary breathing is unequivocal, 

 and, therefore, the better evidence is that of the uni- 

 formity of the laws of nature ; more especially, as all 

 the creatures alluded to are furnished with apparatus 

 for enabling them to ascend to the surface, and many 

 of these have no other apparent use, The germ in 

 nature, be it that of plant or of animal, contains the 

 whole elements of the future being, and there is no 

 well-established instance of any such change, as that 

 from breathing air to breathing water, or the reverse. 



That insects in their chrysalid state may remain 

 under the water, though both the larva and the perfect 

 insect should have to come to the surface at long or at 



