THE PECULIAR FACULTIES 271 



in which water is the respired fluid ; and such again is the respiration 

 of the insects and arachnids, in which the respired fluid is atmospheric 

 air. 



But the respiration of animals, which have a general circulation, is 

 of a very different type ; it is effected more rapidly, it gives rise to 

 special movements which in the highest animals become regular, 

 and it is carried out in a simple, double or compound organ that is 

 isolated and does not spread throughout the body. The essential fluid 

 or blood of the animal then goes beyond the respired fluid, which only 

 penetrates as far as the respiratory organ : the blood therefore has to 

 undergo in addition to the general circulation a special circulation that 

 I may call respiratory. Now since it is sometimes only a part of the 

 blood that travels to the organ of respiration before being despatched 

 throughout the animal's body, and since in other cases the whole 

 of the blood passes through this organ before its journey in the body, 

 the respiratory circulation is accordingly said to be either complete 

 or incomplete. 



Now that I have shown that there are two quite different types of 

 respiration in those animals which have a distinct respiratory organ, 

 I think that the name of general respiration may be given to the first 

 type, such as that of the radiarians, worms, and insects ; and that the 

 name of local respiration should be applied to the second type, which 

 belongs to animals more perfect than insects, including perhaps the 

 limited respiration of arachnids. 



The faculty of breathing is thus peculiar to certain animals ; and 

 the nature of the organ by which they breathe is so well adapted 

 to their needs and to the stage of development of their organisation, 

 that it would be very unreasonable to expect to find in imperfect 

 animals the respiratory organ of more perfect animals. 



The Muscular System. This confers upon the animals which possess 

 it, the faculty of performing actions and movements, and of controUing 

 these activities either by the inclination due to habit, or by the inner 

 feeUng, or, lastly, by the operations of the intellect. 



Since it is admitted that no muscular activity can occur without 

 nervous influence, it follows that the muscular system must have 

 been formed after the rise of the nervous system, at all events in its 

 first outlines. Now if it is true that that function of the nervous 

 system, of which the purpose is to dispatch the subtle fluid of the 

 nerves to the muscular fibres or bundles and set them in action, is 

 much simpler than that other function of producing feeling (as I 

 hope to prove), it must follow that as soon as the nervous system had 

 reached the stage of a medullary mass in which terminate the various 

 nerves, or as soon as it was provided with separate ganglia sending 



