METAMOEPHOSES OF DEAGON-FLY. 349 



although the larva (fig. 176, a, c, d, e,f) has no legs or exterior ap- 

 pendages, in the pupa (b) all the limbs of the perfect Bee are recognized 

 with the utmost facility. Yet all these organs are still enclosed in 

 distinct cases (thecce), to each of which names have been applied by 

 entomological writers ; and it is only on throwing off the integument 

 which thus imprisons the mature insect that the Bee makes its ap- 

 pearance in a capacity to begin its active and industrious existence in 

 the winged state. 



(911.) Those insects whose larva only differs from the imago in not 

 being possessed of wings (fig. 145, c), Eabricius regarded as undergoing 

 a semicomplete metamorphosis; and when the perfect insect did not 

 acquire wings at all, but precisely resembled the pupa, he called the 

 latter complete. 



(912.) But there are innumerable 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. 146, 147), 

 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 wonderful changes occur during the last stage of the metamor- 

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

 to climb the stems of subaquatic plants in search of prey, is possessed 

 of a very peculiar locomotive apparatus whereby it can propel itself 

 through the element which it inhabits. Appended to the posterior ex- 

 tremity 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. 



(913.) But the contrivance above mentioned is also made sub- 

 servient 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 exa- 

 mined 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. 



(914.) Another remarkable peculiarity is met with in the structure 

 of the mouth of these aquatic larvse ; for the oral .apparatus here forms 

 an instrument of prehension adapted to seize prey at a distance, and 

 constitutes, in fact, a kind of projectile forceps of a very curious con- 

 struction. Let the reader contrast the following description with that 

 already given of the oral organs of the Dragon-fly ( 818), and observe 

 * Mem. de la Soc, d'Hisfc. Nat. p. 48. 



