INTERNAL ORGANS. 83 



spots where one would look for spiracles ; it even 

 sends a small tube from opposite the base of each 

 trunk to the point where the neighboring spiracles 

 should be, which, however, disappears with the 

 growth of the animal. Indeed, we may reason- 

 ably believe that in the original form of the larva 

 it possessed complete breathing organs upon these 

 segments, since they differ from the succeed- 

 ing segments only in the want of spiracles and in 

 the slightly smaller size of the tracheal mass, and 

 of the exceedingly short tube which connects it 

 with the spiracles. 



These air tubes ramify and subdivide infinitely ; 

 a great many of them impinge upon the stomach 

 and encircle it in their grasp, serving in fact as 

 its support ; others penetrate all parts of the 

 muscular mass, embrace every organ and track 

 along every thread of nerve or fibre ; those from 

 the first segment behind the head, after first unit- 

 ing with each other so as to make a perfect com- 

 munication between the tracheae of the two sides 

 of the body, send powerful branches from the 

 point of union into every part of the head, where 

 the minute subdivisions pass into the furthermost 

 joints of the antennae, or into the jaws, while 

 every muscle finds one for its nearest neighbor. 



It is not, however, until we come to consider 

 the circulatory system that we can fully under- 

 stand the meaning of this endless ramification of 



