CIRCULATION IN INSECTS. 223 



parts. In the wings, on the other hand, where the 

 developement proceeds rapidly, the circulation 

 becomes more active ; and even after they have 

 attained their full size, and are yet in a soft state, 

 the motion of the blood in the centre of all the 

 nervures is distinctly visible :* but afterwards, as 

 the wings become dry, it ceases there also, and is 

 then confined to the canals of the trunk. In pro- 

 portion as the insect approaches to the completion 

 of its developement, these latter canals also, one 

 after the other, shrink and disappear ; till at length 

 nothing which had once appertained to this sys- 

 tem remains visible, except the dorsal vessel. But 

 as we observe this vessel still continuing its pulsa- 

 tory movements, we may fairly infer that they are 

 designed to maintain some degree of obscure and 

 imperfect circulation of the nutrient juices, through 

 vessels, which may, in their contracted state, corre- 

 sponding to the diminished demands of the system, 

 have generally escaped detection. Minute branches 

 have, by late observers, been traced, proceeding in 

 different directions from the dorsal vessel, and dis- 

 tributed to various organs-t At a more advanced 



* These currents in the wing of the Semblis bilineata have been 

 described and deHneated by Carus, in the Acta Acad. Cses. Leop. 

 Carol. Nat. Cur. vol. xv. part ii. p. 9. 



\ The division of the anterior part of the dorsal vessel into des- 

 cending branches was noticed by Comparetti. Duges has observed 

 a similar division of this vessel in the corselet of several species of 

 FhalencE, and further ramifications in that of the Gryllus lineola: 

 and Audouin has traced them in many of the Hymenoptera. (An- 

 nalesdes Sciences Naturelles, xv. 308.) 



The figures which follow (from 339 to 345) are representations, 

 of the natural size, of the dorsal vessel of the Sphinx Ugustri, or 

 Privet Hawk-moth, which has been dissected in its three different 

 stages, with great care, by Mr. Newport, from whose drawings these 



