278 



HITCHCOCK'S ANATOMY 



gans, as was seen to be the case with birds. Still another 

 way in which respiration is effected, is by the sliding of one 

 ring inside the next one, like the joints of a hand telescope, 

 and their return by the elasticity of the tissues of the body. 

 And we can not fail to observe the beautiful design of the 

 Creator, when, though he furnished but a limited circulation 

 of fluid, yet fully compensated for it by introducing the air in 

 minute tubes to the very center of every tissue. 



489. Crustaceans . — These animals breathe mostly by gills. 

 The Myriapods have proper tracheae, though with some respi- 

 ration is chiefly cutaneous, that is, directly through the skin. 

 The Arachnoid or Spider tribe sometimes have tracheae and 

 sometimes even lungs. The gills of the Crustaceans are situ- 

 ated in different parts of the body, more especially on the 

 feet. 



490. Molluscs. — In the Acephala the blood before return- 

 ing to the heart passes through a bronchial organ or gill, 

 which opens and closes for the ingress and egress of water. 

 Some of the Cephalophora have gills ; others lungs, and others 

 a system for the circulation of water containing air, through 

 different parts of the body. The Cephalopoda all respire by 

 gills ; but they have also an aquiferous system. 



491. Radiates. — "The simple exposure of the surface of 

 a jelly-fish or polyp to the action of the fluid around it is 

 sufficient to carry on all the changes which take place in its 

 simple kind of respiration." — Prof. J. Wyman. Nearly all 

 the Radiates have such an aquiferous system. But many 

 of them have other organs for breathing. The Echinoderms 

 have gills; also sometimes their organs of prehension and 

 locomotion form a respiratory apparatus. 



"What instance of compensation is shown here ? 480. Do any crustaceans breathe by 

 gills ? 490. What is the breathing apparatus of molluscs ? 491. What is xhe respiratory 

 apparatus of radiates ? 



