244 THE VITAL FUNCTIONS. 



of the trunk. In proportion as the insect ap- 

 proaches to the completion of its developement, 

 these latter vessels also, one after the other, shrink 

 and disappear ; till at length nothing which had 

 once appertained to this system remains visible, 

 except the dorsal vessel. But as we observe 

 this vessel still continuing its pulsatory move- 

 ments, 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, correspond- 

 ing to the diminished demands of the system, have 

 generally escaped detection. In confirmation of 

 these views it may be stated, that several ob- 

 servers have, at length, succeeded in tracing 

 minute branches, proceeding in different direc- 

 tions from the dorsal vessel, and distributed 

 to various organs. The division of the anterior 

 part of the dorsal vessel into descending branches 

 was noticed by Comparetti. Dug^s has observed 

 a similar division of this vessel in the corselet of 

 several species of Phalence^ and further ramifica- 

 tions in that of the Gryllus lineola: and Audouin 

 has traced them in many of the Hymenoptera.* 



* Annales des Sciences Naturelles, xv. 308. 



The figures which follow (from 339 to 345) are represen- 

 tations, of the natural size, of the dorsal vessel of the Sphinx 

 ligustri, or Privet Hawk-moth, which has been dissected in its 

 three diflerent stages, with great care, by Mr. Newport, from 



