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. Duges has observed 

 a similar division of this vessel in the corselet of 

 several species of Phalence, and farther 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 different stages, with great care, by Mr. Newport, from 



