290 INSECTA. 



Those insects whose larva only differs from the imago in not 

 being possessed of wings (Jig. 102), Fabricius regarded as under- 

 going a semi-complete metamorpho- pig. 132. 

 sis ; and when the perfect insect did 

 not acquire wings at all, but pre- 

 cisely resembled the pupa, he called 

 the latter complete. 



(338.) But there are innumer- 

 able examples of metamorphosis 

 which will not conform to any of 

 the above definitions, and in some 

 of them the phenomena exhibited 

 are not a little remarkable. We 

 have already mentioned the changes 

 which the dragon-fly undergoes 

 (figs. 103, 104), and have seen 

 that in this case there is no very 

 striking resemblance between the 



pupa and the adult creature, but, on the contrary, that very won- 

 derful changes occur during the last stage of the metamorphosis. 

 The pupa lives in water ; and, besides six jointed legs adapted to 

 climb the stems of subaquatic plants in search of prey, is pos- 

 sessed of a very peculiar locomotive apparatus, whereby it can 

 propel itself through the element which it inhabits. Appended to 

 the posterior extremity of the abdomen we find three or five leaf- 

 like appendages, which the creature continually opens and closes, 

 and at the same time takes in a quantity of water, sufficient to 

 fill the muscular termination of the rectum, which is expanded for 

 the purpose ; this water is, at intervals, forcibly expelled, mingled 

 with bubbles of air, and thus effects the propulsion of the animal 

 by a mechanism which human ingenuity has imperfectly attempted 

 to imitate, 



But the contrivance above mentioned is also made subservient to 

 respiration ; for, from the observations of Cuvier,* it appears that 

 the interior of the rectum exhibits to the naked eye twelve longi- 

 tudinal lines of black spots arranged in pairs ; and these, when ex- 

 amined under the microscope, are found to be composed of little 

 conical tubes, from which branches go off to join the principal 

 longitudinal tracheae that distribute air through the body. 



Another remarkable peculiarity is met with in the structure of 



* M6m. de la SociSte d'Histoire Nat. p. 48. 



