476 



THE MICROSCOPE. 



will often spring from the table from mere elasticity, and 

 thus the labour of hours be lost in a moment. It does 

 not appear to me desirable to attempt to flatten an entire 

 cornea by pressure and maceration, although this is gene- 

 rally recommended, as it does not either aid in developing 

 the beauty, or counting the number of its lenses. On the 

 contrary, the rounded membrane becomes, if the margin 

 remains intact, corrugated; and so one hexagon overlaps 

 the other. It will be useful, therefore, to make two pre- 

 parations of the eyes of one insect : the one entire, retain- 

 ing its natural curved form, not having been subjected to 

 pressure ; the other nicked at its margin, or cut into small 

 fragments, and pressed between two slides. 



" Each hexagon forms the slightly horny case of an eye. 

 Their margins of separation are often thickly set with hair, 

 as in the Bee ; in other instances naked, as in the Dragon-fly, 

 House-fly, &c. The number of these lenses have been calcu- 

 lated by various authors, and their multitude cannot fail to 

 excite astonishment. Hooke counted 

 7,000 in the eye of a House-fly; 

 Leeuwenhoek more than 12,000 in 

 that of a Dragon-fly; and Geoffry 

 cites a calculation, according to which 

 there are 34,650 of such facets in 

 the eye of a Butterfly." 1 



The trunk is situated between the 

 head and the abdomen; the legs 

 and wings are inserted into it. The 

 thorax is the upper part of the 

 trunk; the sides and back of which 

 are usually armed with points or 

 hairs. The abdomen forms the pos- 

 terior part of the body, and is 

 generally made up of rings or seg- 

 . ments, by means of which the insect 

 lengthens or shortens itself Running 

 along the sides of the abdomen are 

 the spiracles, or breathing apertures, fig. 237, commu- 

 nicating directly with the internal respiratory organs. 

 Pure air being thus freely admitted to every part, and the 



(1) John Gorham, Esq., MicroscopicalJournal, 1853. 



