CIRCULATORY ORGANS, 29 



by tlie action of the muscular fibres of its own coats. 

 By this means the chambers formed by the folding in 

 of the membranes contract and expand one after the 

 other, commencing with the hindmost_, and the blood, 

 which is drawn in through the lateral openings, is thus 

 driven successively through all the chambers until it 

 issues from the orifice at the head. But here we meet 

 with something rather unexpected, for the blood, in- 

 stead of finding a set of arteries ready to receive it 

 and distribute it to all the organs of the body, is 

 simply poured out amongst the tissues and finds its 

 way back again into the abdomen through the spaces 

 left between the internal organs. It is indeed forced 

 to follow a tolerably determinate course, as the greater 

 part of the cavity of the body is filled up with masses 

 of a fatty matter, and it is through the interstices of 

 this that the blood flows. With the exception of the 

 dorsal vessel, in fact, there is no such thing as a true 

 vessel in the body of an insect, for there is no evidence 

 that the tubes found in the veins of the wings are 

 fm-nished with regular membranous walls. 



From this absence of vessels it is evidently impos- 

 sible that the nutritive matter prepared for assimila- 

 tion in the intestinal canal, should be absorbed and 

 carried into the system in the same way as in the 

 higher animals, where we find a regular system of 

 vessels appropriated to this function; in the Insects 

 this operation is efi'ected in a very simple manner : the 

 liquefied portions of the food pass through the coats 

 of the intestine, and thus mingle directly with the 

 ready-formed blood which bathes its outer surface. 

 The blood, as is well known, is nearly colourless, and 

 the numerous corpuscles which it contains are also 

 destitute of colour. 



