108 NATURAL HISTORY 



aorta, but many ; all going out from the long canal of the heart. 

 Whatever blood is sent out from the heart in the insect is prepared 

 blood ; therefore the arteries serve the purpose of the aorta ; and the 

 veins, both of the veins in common, as also those called pulmonary [in 

 the Tetracoilia] ; for the common veins have the blood prepared in 

 them, serving the purpose of pulmonary veins in the insect. 



I conceive that there is a great regularity in the vascular system in 

 the insect, although it is not easily unravelled. 



Of the Arteries. — The arteries would appear to go out laterally, 

 in a kind of plexuses 1 , and would appear to form the same on the 

 stomach, &c. 



Of the Veins. — The veins of the insect would appear to be simply the 

 cellular membrane ; but they are regular formed canals, although not 

 such distinct cylindrical canals as in the quadruped, &c, nor branching 

 with that regularity. They would appear to be, or to fill up, the inter- 

 stices of the flakes of fat, air-cells, muscles, &c, and therefore might 

 be called in some measure the cellular membrane of the parts 2 . 



Of the Respirator-y Organs of the Flying Insect. 



The organs of respiration of the flying insect answer two purposes ; 

 one, the purifying the blood, the other for flying. 



It is probable that they are much too large for the first use ; for, in 

 the beetle they are much larger than in the fly, because it is much 

 heavier in the body ; therefore the beetle requires more of those organs 

 to give it levity [and has wider and more numerous air-cells]. 



Of the Water Spider (Hydrachna). 



Observing a small spider in the water where I had two cuttle-fishes 

 crawling about, I took it out, and put it into [another vessel of] water ; 

 and it lived there very well for above two weeks. It laid its eggs and 



1 [The parts here described answer best to the attaching muscles, or 'aliform 

 ligaments' of Straus Durckheim, and to the entering sinuses, of the heart.] 



2 [Cuvier supposed the whole of the blood of insects to be limited to receptacles 

 of this description, and consequently denied that they possessed a true circulation, 

 or that the dorsal tube acted as a heart. The more accurate views of Hunter, based 

 on the analogy of the already commencing irregularity and extent of the venous 

 sinuses in the crustaceans, have been amply confirmed by the researches of Prof. 

 Carus, on the ; Circulation of the Blood in the Larva' of Ephcmcrides and Libellulce.' 

 See Bhdkreislaufes in den Larven netzfliiglicher Insecten, 4to. 1827. See my 

 ' Preface to the Animal Economy.' p. 22 ; and ' Physiological Catalogue,' 4to. vol. ii. 

 p. 31.] 



