OF THE BLOOD-VESSELS. 187 



is situated in the anterior part of the trunk ; through the 

 heart the whole of the blood contained in the body is sup- 

 posed to pass : all the arteries and veins originate or ter- 

 minate in the heart : the arteries and veins are the organs 

 of circulation. We find, that in insects, there is no part 

 positively ascertained to be the heart ; but we discover 

 blood circulating throughout the body, and we trace it to 

 a series of large reservoirs, which form a connected line or 

 channel the whole length of the insect. 



The blood of insects is a thin, transparent, and almost 

 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. The best objects 

 in which to observe the circulation of this blood, are trans- 

 parent aquatic larva?, more particularly those of Eplie- 

 mer(B ; and these being distinctly divided into the usual 

 thirteen segments, afford us also the means of establishing 

 a nomenclatm-e. The number of reservoirs composing the 

 great channel in Ephemera is twelve, one to each of the 

 segments, except the head ; these, not having been hitherto 

 named, may be called little hearts or corcula, and each one 

 may be designated by the name of the segment in which 

 it is situated, as the corcuJum of the telum or teli corcu- 

 hmi, but it must be distinctly understood that the number 

 of corcula by no means invariably agrees with that of the 

 segments ; on the contrary, it has been established beyond 

 question, that the number of corcula is, in most perfect 

 insects, inferior to that of the segments. In this case the 

 anterior portion of the channel being without divisions, 

 has been supposed analogous to the aorta, and called by 

 that name. Each corculum is somewhat pear-shaped, the 

 smaller or pointed extremity being directed towards the 

 head of the insect, and fitting into a cavity in the corculum 



