INSECTS. 295 



insects in the larva and perfect states were found to leave any visible 

 track behind them when they crawled over glass ; and, by the aid 

 of powerful magnifying-glasses, it was found that traces were left of 

 an exceedingly minute quantity of glutinous matter, which appeared 

 to have been emitted by the feet of these creatures ; and subsequent 

 experiments proved that the hair-like appendages which form the 

 brushes of spiders and flies are all tubular. 



Plate VIII. represents the tongue and piercing apparatus of the 

 Droiw Fly. This remarkable compound structure, together with the 

 admirable form and exquisite beauty of the apparatus, must strike the 

 mind with wonder and delight, and lead the observer to reflect on the 

 weakness and impotence of all human mechanism, when compared 

 with the skill and inimitable finish displayed in the object before us. 

 The fleshy outer case which encloses it has been removed for the 

 purpose of viewing the several parts, which consist of two spongy 

 guards or feelers, covered with short hairs, united to the head by 

 muscles ; these feelers appear to be merely used as a preservative 

 apparatus, in guarding the organs from external injury. The two 

 lancets seen above them are formed somewhat like a cutlass, or the dis- 

 secting knife of the anatomist, and purposely intended for making a 

 deep and sharp cut, and also for cutting vertically with a sweeping 

 stroke. The other and larger cutting instrument appears to be in- 

 tended to enlarge the wound, if necessary ; or it may be for the 

 purpose of irritating and exciting the part around, thereby increasing 

 the flow of blood to the part, being jagged or toothed at the extremity. 

 The larger apparatus, with its three peculiar prongs or teeth, is tubu- 

 lar, to permit the drawing up of the blood and conveying it to the 

 stomach ; it is enclosed in a case which entirely covers it. The spongy 

 tongue itself projects some distance beyond this apparatus, and is 

 composed of a beautiful network of soft muscular spiral fibres, forming 

 a series of absorbent tubes ; and these are moved by powerful muscles 

 and ligaments, the retractile character of which may be there seen in 

 the drawing of the proboscis of the fly, Plate VII. : by the aid of these 

 booklets he is enabled to draw in and dart out the tongue with won- 

 derful rapidity. The striated appearance of another set of muscles may 

 be seen at the root of the whole. 



" In the organisation of the mouth of various insects we have a 

 modification of form, to adapt them to a different mode of use ; as in 

 the Muscidce, or common house-flies. When the food is easily acces- 

 sible, and almost entirely liquid, the parts of the mouth are soft and 

 fleshy, and simply adapted to form a sucking tube, which in a state of 



