OF THE ANNULOSA. 409 



two branches, which are adorned with plumose sub- 

 divisions ranged parallel to their axes. Then comparing 

 this structure with the wings of the Pterophori, a small 

 family of Lepidoptera, of which the wings are composed 

 of feathers somewhat similar to those of a bird, he con- 

 cludes that the feet in the Caligus are the substitutes of 

 wings, and that the wings in the Omeodes occupy the 

 place of feet. Without prejudice to the validity of his 

 conclusion, it may however be properly objected to this 

 mode of reasoning, that the general construction of the 

 Orneodes being so distant from that of Caligus, we 

 cannot place much faith in any affinity between the details. 

 M. Latreille seems to perceive this, and therefore adopts a 

 closer but scarcely more solid comparison, in assimilating 

 the tracheal fins of the larvae of Ephemeridce to the wings 

 of the perfect insect, that is, abdominal to thoracic appen- 

 dages, and then appeals to the observations of M. de 

 Blainville, which prove that the wings of Insects are a 

 sort of tracheae*. On these loose notions of resemblance 

 he founds his opinion that the wings of a Hexapod insect 

 are nothing else than tracheal appendages, which occupy 

 the place of tarsi in certain feet. The articulations of 

 the wings which correspond to the coxa, femur, and tibia, 

 are, in his judgement, so far rudimentary that he hesi- 

 tates to give these names to the three or four callosities, 

 termed osselets by M. Jurine, which, although nearly con- 

 cealed in the thoracic cavity, are visible at the root of a 

 wing. M. Latreille was doubtless carried a great way to- 

 wards this conclusion on still more solid ground than has 

 been just cited, namely, a Memoire on the Wings of Insects, 



* This discovery ought not to be attributed to M. de Blainville, but to 

 the late M. Jurine, who in the introduction to his work on Hymenoptera 

 has admirably explained the structure of their wings. 



