580 RESPIRATION A MEASURE 



guid, the arteries small and few, the blood pale 

 and watery, the muscles flaccid, the bones soft, 

 or replaced by cartilage, while the brain consists 

 of a few small knots or ganglions, with a corres- 

 ponding defect of the senses.* And notwith- 

 standing they move with great velocity through 

 water, it is owing to the density of that medium, 

 by which they are enabled to propel themselves 

 onward by a small exertion of vital force ; nearly 

 all of which that they possess is expended on the 

 muscles employed in locomotion. But as Cuvier 

 observes, they are soon exhausted by exertion, 

 which is true of all cold blooded animals. 



As a further proof that the aggregate vital 

 energy of all animals is directly in proportion to 

 the developement of their breathing apparatus, it 

 may be added, that by means of stigmata or holes, 

 arranged along their bodies, and minute vesicles 

 for conveying air throughout the system, the 

 active insects are more fully supplied with organs 

 of respiration than any other description of ani- 

 mals, not excepting birds. As an example of the 

 large amount of oxygen they consume, Spallan- 

 zani found that a caterpillar generated more 

 carbonic acid in a given time than a frog, and 



* The eyes are without lustre, the organs of hearing scarcely 

 distinguishable, and so imperfect are those of voice, that they 

 have no power of uttering sounds, but vegetate in perpetual dumb 

 silence, without even the animal desire of sexual communion, or 

 the slightest regard for their offspring. 



