652 



CHAPTER XVII. 



INSECTS AND ARACHNIDA. 



There is no Class in the whole Animal Kingdom which affords to 

 the Microscopist such a wonderful variety of interesting objects, 

 and such facilities for obtaining an almost endless succession of 

 novelties, as that of Insects. For, in the first place, the number 

 of different kinds that may be brought-together (at the proper 

 time) with extremely little trouble, far surpasses that which any 

 other group of Animals can supply to the most painstaking Col- 

 lector : then, again, each Specimen will afford, to him who knows 

 how to employ his materials, a considerable number of Microscopic 

 objects of very different kinds; and, thirdly, although some of 

 these objects require much care and dexterity in their preparation, 

 a large proportion may be got-out, examined, and mounted, with 

 very little skill or trouble. Take, for example, the common House- 

 Fly : — its Eyes may be easily mounted, one as a transparent, the 

 other as an opaque object (§ 517) ; its Antennce, although not such 

 beautiful objects as those of many other Diptera, are still well worth 

 examination (§ 518); its Tongue or 'Proboscis' is a peculiarly 

 interesting object (§ 519), though requiring some care in its pre- 

 paration ; its Spiracles, which may be easily cut-out from the sides 

 of its body, have a very curious structure (§ 525) ; its Alimentary 

 canal affords a very good example of the minute distribution of the 

 'Tracheae' (§ 524); its Wings, examined in a living specimen 

 newly come-forth from the Pupa state, exhibit the Circulation of 

 the blood in the • Nervures ' (§ 523) ; the Wing of this Insect, 

 when dead, moreover, exhibits a most beautiful play of Iridescent 

 colours, and shows a remarkable Areolation of surface, when it is 

 examined by light reflected from its surface at a particular angle 

 (§ 528) ; its Foot has a very peculiar conformation, which is doubt- 

 less connected with its singular power of walking over smooth 

 surfaces in direct opposition to the force of gravity, although the 

 mode in which it serves this purpose is not yet certainly ascer- 

 tained (§ 530) ; and the structure and physiology of its Sexual 

 apparatus, with the history of its Development and Metamor- 

 phoses, would of itself suffice to occupy the whole time of an 



