IMPERFECT PERFECT INSECTS. 205 



of these animals has arrived at its perfect state or not ; and 

 hence, as Fabricius observed in his Philosophia Entomologica, 

 it is probable that many supposed species of spiders, &c., 

 have been formed out of the immature states of these animals. 



There are, however, some insects belonging in reality to 

 the winged tribes, which form an exception by being destitute 

 of wings in the perfect state : such are the bed bugs, many 

 individuals of Velia, Hydrometra, and Gerris, likewise 

 numerous Phasmida, and other apterous Orthoptera and 

 Hemiptera. 



2. Of those species which undergo the metamorphosis 

 dimidiata of Latreille, the pupa has been most appropri- 

 ately termed semi-complete by Linnaeus ; we therefore Can- 

 not approve of the alteration of this term to sub-incomplete, 

 proposed by Burmeister ; the pupa being intermediate be- 

 tween the larva, in which the body is completely apterous, 

 and the imago, in which it is furnished with fully-developed 

 wings ; and being active like the larva, but provided with 

 these organs, but so wrapt up as to be easily inclosed within 

 four short cases, which arise in pairs from the back of the 

 second and third segments of the body. Here belong the 

 tribes of locusts, grasshoppers, mantes, cockroaches, ear- 

 wigs, bugs, and treehoppers, in all which the resemblance of 

 the pupa to the imago is very distinct. Here, also, are gene- 

 rally arranged the dragon-flies and the may-flies (Ephemerae}, 

 but in these groups the likeness of the pupa to the imago is 

 less distinct, the organs of respiration being quite different, 

 as above noticed, and the structure of the mouth being 

 totally dissimilar. These groups, accordingly, are said by 

 Mr. MacLeay to undergo a sub- semi-complete metamor- 

 phosis. There is another peculiarity connected with this 

 species of metamorphosis, which sufficiently proves that 

 here we are intermediate between the merely rudimental 

 and the perfect metamorphosis, and that the perfection of 



