THE METAMORPHOSIS. 421 



clouds, and swims in the fluid element. The majority are inimical to 

 water : a few only seek it and dwell in it. 



A very similar series of developments to those just observed in the 

 Malacostraca, do we find in the pupa of insects with a perfect meta- 

 morphosis. The lowest^ as the pupa of the gnats, some other Diptera, 

 and the Phryganece, breathe like the Crustacea through gills, but 

 their number is small compared with the large order of the Crustacea, 

 which thence proceeds that they merely briefly indicate this order, 

 and are not intended fully to repeat it. All other pupa breathe through 

 spiracles. Some of them, as the pupae of the flies, crepuscular moths, 

 and beetles, lie in the earth ; they represent the Myriapoda, of which 

 many but rarely visit the light of day, but dwell beneath stones and 

 in other shady places. The pupae of the butterflies and Noctuce seek, 

 on the contrary, the air, particularly those which hang themselves 

 freely in the air, that they may enjoy it upon all sides. Those that 

 are affixed may, lastly, be compared with the spiders that float in their 

 webs. 



With respect to their internal organisation, the imperfect simple 

 tubular form of the entire intestinal canal, the predominance of the 

 circulation in all parts, as well as the mere rudiments of the sexual 

 organs, evince the analogy of the larvae to the Annulata. The per- 

 fecting of the intestinal canal during the pupa state, particularly the 

 formation of the proventriculus at this period, and, lastly, the more 

 distinctly developed sexual organs, although the latter conditionates 

 no significant external difference, still further prove the analogy of 

 the pupa and the Malacostraca. 



We have thus shown the repetition of the lower grades in the 

 development of insects with a perfect metamorphosis. But this entire 

 repetition has been expressed by Oken in the following words * : 

 " Every fly creeps as a worm out of the egg ; then by changing into 

 the pupa, it becomes a crab, and, lastly, a perfect fly. " 



251. 



We have as yet taken no notice of insects with an imperfect 

 metamorphosis, and, indeed, because they are not subjected to the law 

 of repetition or analogy which is so distinctly expressed in insects with 

 a perfect metamorphosis ; for moulting is no metamorphosis, although 



* Naturgeschichte fur Schulen, p. .577. 9th Class and pp. 581, 583. 



