90 Mr. Westwood's Observations 



Other portions of the stinicture of these insects are not less in- 

 teresting. The simple construction of the eyes, formed of a few 

 ocelli alone in some of these insects, as in the lulidce, whilst in others 

 they are short and perfectly reticulated ; — the composition of the 

 body, as in the typical Annulosa ; but more especially the beautiful 

 scales with which the body is covered, and the singular apparatus 

 with which the tail is furnished, whereby the insect is enabled to 

 leap to very considerable distances, and especially the peculiar or- 

 gans with which the underside of the abdominal segments are fur- 

 nished, and which being evidently the analogues of the false legs of 

 the Scolopendra, prove the near approach made by these animals to 

 the Myriapoda, — all deserve notice ; but a more important peculiarity 

 exists in the apparent want of spiracles along the sides of the body, 

 and which Latreille, notwithstanding a very minute examination, 

 was unable to discover. 



There is still another circumstance which renders these insects 

 especially interesting to the naturalist in general, resulting from 

 those principles of natural arrangement which Mr. MacLeay has 

 laid down in the ' Horae Entomologicse'. Thus, if we consider those 

 annulose animals which are the least perfectly organized as forming 

 a distinct class, containing within itself types not only of the other 

 great divisions of the class, but also of each of the various subdivi- 

 sions, we shall find the Thysamira holding an important place with 

 respect to the distribution of the Annulosa in general. Thus they 

 have been regarded by Mr. MacLeay as determining the situation of 

 the Orthoptera amongst mandibulated insects, and of the Amphipoda 

 amongst the Crustacea, on account of the saltatorial powers possessed 

 in common by these different groups, and the setiform appendages of 

 the tail. So in the groups into which the different orders are divided. 

 Ichneumon, Gryllus, Perla, Tenthredo, and Panorpa are placed in ana- 

 logous connexion, on account of the caudal appendages which they 

 possess in common with the Thysanura. 



In like manner, in the distribution of the Coleoptera into five 

 groups, one of them is regarded as analogically representing the 

 Thysanura, on account of the abdominal appendages of the body, al- 

 though this group is but very slightly defined ; whilst in the Lepi- 

 doptera Dr. Horsfield, by applying the same principles, has considered 

 such genera as Apatura, Paphia, Hipparchia, &c. as analogically re- 

 presenting the Thysanura, especially in consequence of the two very 

 strongly marked lengthened filiform or spinous appendages with 

 which the abdomen of the larvae is furnished. 



And the same principle has been carried to a still further extent by 

 Mr. Swainson in his ' Zoological Illustrations,' in which work it is 



