PHYSIOLOGY OF INSECTS. 151 



insect, through every one of the segments, may be 

 most distinctly traced, and the course of veins 

 also intermingling with them. Both kinds of 

 vessels are proportionately much larger than in 

 vertebrated animals : in the interior their limits 

 are vague and difficult to define, but in the lateral 

 portions their exact course is readily ascertained. 



571. The grand veins are twenty-four in number, 

 two opening into each corculum ; those which open 

 into the eleven upper corcula seem to have almost 

 an infinity of supplementary branches, extending 

 little beyond a single segment ; while those of the 

 two last corcula flow from the head itself, through- 

 out the whole length of the insect. 



572. In the setiform appendages of the telum, 

 the circulation is strikingly exhibited : here the 

 ascending artery and descending vein accompany 

 each other; and at the same instant the blood 

 ascends an artery with the usual pulsatory motion, 

 it is flowing in like manner down the vein. 



573. In the nervures of the wings of insects, 

 the course of the arteries and their attendant veins 

 are readily traced : the femora and tibiae also have 

 a most distinct flowing and returning current ; in 

 fact, there is no part of an insect in either the 

 larva or imago state, provided the microscope can 

 reach it, but exhibits most distinctly the circulation 

 and pulsation of the blood. 



