PHYSIOLOGY OF INSECTS. 147 



CHAPTER IX. 



OF THE ORGANS OF CIRCULATION. 



555. IN vertebrated animals the heart is situ- 

 ated in the anterior part of the trunk ; through 

 the heart the whole of the blood contained in the 

 body is supposed to pass: all the arteries and 

 veins originate or terminate in the heart: the 

 arteries and veins are the organs of circulation. 



556. We find, that in insects, there is no part 

 positively ascertained to be the heart; but we 

 discover blood-vessels throughout the body, and 

 we trace them to a series of large reservoirs, which 

 form a connected line or channel the whole length 

 of the insect. 



557. The blood of insects is a thin, transparent, 

 colourless fluid ; it contains a quantity of oval 

 particles which appear perfectly consistent, yet 

 are as transparent as the fluid portion: a small 

 portion of the blood dried on a glass presents a 

 crystallized appearance. 



558. The best objects in which to observe the 



L2 



