VOL. LXXVII.] PHILOSOPHICAL TRANSACTIONS. SOQ 



have come under my own observation. From some circumstances in their di- 

 gestive organs we should be led to suppose, that they were nearly allied to each 

 other ; and that there was not the same variety, in this respect, as in land 

 animals. 



In the description of this order of animals, I shall always keep in view their 

 analogy to land animals, and to such as occasionally inhabit the water, as white 

 bears, seals, manatees, &c. with the differences that occur. This mode of re- 

 ferring them to other animals better known, will assist the mind in understanding 

 the present subject. It is not however intended in this paper to give a particular 

 account of the structure of all the animals of this order, which I have had an op- 

 portunity of examining : I propose at present chiefly to confine myself to general 

 principles, giving the great outlines as far as I am acquainted with them, minute- 

 ness being only necessary in the investigation of particular parts. In my account 

 I shall pay some attention to the relations of men who have given facts without 

 knowing their causes, whenever I find that such facts can be explained on true 

 principles of the animal economy, but no further. 



This order of animals has nothing peculiar to fish, except living in the same 

 element, and being endowed with the same powers of progressive motion as those 

 fish that are intended to move with a considerable velocity : for I believe, that all 

 that come to the surface of the water, which this order of animals must do, have 

 considerable progressive motion ; and this reasoning we may apply to birds ; for 

 those which soar very high have the greatest progressive motion. Though in- 

 habitants of the waters, they belong to the same class as quadrupeds, breathing 

 air, being furnished with lungs, and all the other parts peculiar to the economy 

 of that class, and having warm blood ; for we may make this general remark, 

 that in the different classes of animals there is never any mixture of those parts 

 which are essential to life, nor in their different modes of sensation. 



I shall divide what is called the economy of an animal, first, into those parts 

 and actions which respect its internal functions, and on which life immediately 

 depends, as growth, waste, repair, shifting or changing of parts, &c. the organs 

 of respiration and secretion, in which we may include the powers of propagating 

 the species. 2dly, Into those parts and actions which respect external objects, 

 and which are variously constructed, according to the kind of matter with which 

 they are to be connected, whence they vary more than those of the first division. 

 These are the parts for progressive motion, the organs of sense and the organs of 

 digestion ; all which either act, or are acted on, by external matter. 



This variation from external causes in many instances influences the shape 

 of the whole, or particular parts, even giving a peculiar form to some which be- 

 long to the first order of actions, as the heart, which in this tribe, in the seal, 

 otter, &c. is flattened, because the chest is flattened for the purpose of swimming. 



