INSECTA. 355 



as in the larvae of the Ephemera, from the tergal arch of the segment, 

 and co-exist with rudimental legs from the ventral arch of the same 

 segment. 



WeU, therefore, has the deep-thinking Oken * called the wings of 

 insects "aerial gills ;" they are, in fact, the homologues of the tergal 

 branchiae of the vermiform Articulata, raised to a higher function in 

 correlation with a generally transmuted state of the rest of the orga- 

 nisation, which is advanced to the utmost perfection of which the 

 Articulate type of structure is susceptible. And have we not already 

 seen the membranous aliform branchiae of the beetle protected, like 

 the gills of the lobster, by an elytral carapace developed from a more 

 advanced segment ? Have we not likewise found the metamorphosed 

 branchial wings of the Pterophora subdivided lengthwise like the 

 tufted tergal gills of the Nereis ? 



The air-breathing articulated animals with jointed legs offer a 

 close correspondence with those that respire by gills in the progres- 

 sive steps of complication of the nervous system and the order in 

 which those steps succeed each other. The lowest insects, like the 

 lowest Crustaceans, resemble the worms, in the great length and 

 slenderness of their body, and in the uniform size, shape, and number 

 of the constituent segments. In the lulus {Jig. 140.), whose very 

 short and numerous rings support each two pairs of rudimental legs, 

 the corresponding ganglions of the abdominal chords are much less 

 conspicuous than in the earth-worms, and the whole central axis of 

 the nervous system, continued from the brain, is almost as devoid of 

 partial swellings as the spinal chord of the apodal vertebrate. It 

 lies, however, as in other Articulata, on the opposite side of the 

 body to that in which the brain is situated. 



The cephalic ganglion {Jig. 144, a) of the lulus is transversely 

 elongated, and obscurely divided by a slight median indentation into 

 two side-lobes : its upper and latter extremities are prolonged out- 

 wards into the short and thick optic nerves (c, c), which resolve 

 themselves half way towards the compound eye into a plexus of fila- 

 ments for its several divisions. Two separate antennal nerves, con- 

 jectured by Straus to be motory and sensory {d^ cT), are sent off on 

 each side below and in front of the optic nerves to the short seven- 

 jointed antennae. On each side also, but below the antennal nerves, 

 arise the two nerves {h) united together by an anastomosing branch 

 which supply the palpless mandibles. 



The thick oesophageal chords {g) are continued from the posterior 

 and inferior angles of the brain ; and, though apparently simple, 



* Natur. Philosophic, 2d Ed. p. 418. 

 A A 2 



