CIRCULATION IN INSECTS. 177 



which may, in their contracted state, corresponding to the 

 diminished demands of the system, have generally escaped 

 detection. In confirmation of these views, it may be stated, 

 that several observers have, at length, succeeded in tracing 

 minute branches, proceeding in different directions, from the 

 dorsal vessel, and distributed to various organs. The divi- 

 sion of the anterior part of the dorsal' vessel into descending 

 branches -was noticed by Comparetti. Duges has observed 

 a similar division of this vessel in the corselet of several spe- 

 cies of Phalenae, and farther ramifications in that of the 

 Gryllus lineola: and Audouin has traced them in many of 

 the Hymenoptera.* 



* Annales des Sciences Nat.urelles, xv. 308. 



The figures which follow (from 339 to 345) are representations, of the na- 

 tural size, of the dorsal vessel of the Sphinx ligustri, or Privet Hawk-moth, 

 which has been dissected in its three different stages, with great care, by 

 Mr. Newport, from whose drawings these figures have been engraved, and 

 to whom I am indebted also for the description which follows: 



The dorsal vessel of this insect is an elongated and gradually tapering ves- 



339 



344 



sel extending from the hinder part of the abdomen, along the back, towards 

 the head; and furnished with valves, which correspond very nearly in their 

 situation to the incisions of the body. During the changes of the insect 

 from the larva to the imago state, it undergoes a slight modification of form. 

 In every state it may be distinguished into two portions, a dorsal and an cor- 

 VOL. II. 23 



