424 SIR J. LumiocK on the origin ok insects. 



insect from feeding for a time, as, for instance, ia the case with the 

 silkworm. When, however, any considerable change was in- 

 volved, this period of fasting would be prolonged, and would lead 

 to the existence of a third condition, that of the pupa, intermediate 

 between the otlier two. Since other changes are more conspi- 

 cuous than tliose relating to the mouth, we are apt to associate 

 the pupa-state with the acquisition of wings : but the case of the 

 Orthoptera (grasshoppers &c.) is sufficient proof that the de- 

 velopment of wings is perfectly compatible with continuous 

 activity ; so that in reality the necessity for rest is much more 

 intimately connected with the change in the constitution of the 

 mouth, although in many cases no doubt the result is accom- 

 panied by changes in the legs, and in the internal organization. 

 It is, however, obvious that a mouth like that of a beetle could 

 not be modified into a suctorial organ like that of a bug or a gnat, 

 because the intermediate stages would necessarily be injurious. 

 Neither, on the other hand, for the same reasons, could the 

 mouth of the Hemiptera be modified into a mandibulate type 

 like that of the Coleoptera. But in Campodea and the Collem- 

 bola we have a type of animal closely resembling certain larv£e 

 which occur both in the mandibulate and suctorial series of 

 insects, and possessing a mouth neitlier distinctly mandibulate 

 nor distinctly suctorial, but constituted on a peculiar typo capable 

 of modification in either direction by gradual changes without 

 loss of utility. 



Before concluding, I must say a few words about the probable 

 nature and origin of the wings. Whence are they derived ? why 

 are there normally two pairs ? and why are they attached to the 

 meso- and metathorax? These questions are not less difficult 

 than interesting. It seems to me that the wings of insects origi- 

 nally served for aquatic and respiratory purposes. From the 

 various modes by which respiration is efliected among the difl^er- 

 ent groups of aquatic insects, we are justified in concluding that 

 the original insect stock was, like Campodea, a laud-animal. But 

 in aquatic insects there is a tendency to effect the purification of 

 the air through the delicate membranous covering of more or less 

 foliaceous expansions of the skin. In the larva of Chloeon, for 

 instance, which singularly resembles Campodea, several of the 

 segments are provided with such foliaceous expansions, which, 

 moreover, are in constant agitation, and the muscles of which, in 

 several remarkable points, resemble those of the true wings. It 



