295 THE PHILOSOPHY 



change their Ikins oftener or more feldom, according to the 

 fpecies. Malpighius informs us, that the filk-vvorm, pre- 

 vious to its chryfahs flate, cafts its fltin four times. The 

 firft fkin is caft on the 10th, 11th, or l^ith day, according to 

 the nature of the feafon •, the fecond in live or fix days after •, 

 the third in five or lix days more ; and the fourth and laft 

 in fix or feven days after the third. This changing of ikin 

 is not only common to all caterpillars, but to every infe£t 

 whatever. Not one of them arrives at perfection vi^ithout 

 cafting its flvin at leaft once or twice. The lliin, after it is 

 call, preferves fo entirely the figure of the caterpillar in its 

 head, teeth, legs, colour, hair, &c. that it is often miftaken 

 for the animal itfelf. A day or two before this change hap- 

 pens, caterpillars take no food : They lofe their former ac- 

 tivity, attach themfelves to a particular place, and bend their 

 bodies in various dire£i:ions, till at laft they efcape from the 

 old ikin, and leave it behind them. The inteftinal canal of 

 caterpillars is compofed of two principal tubes, the one in- 

 ferted into the other. The external tube is compact and 

 flefhy ; but the internal one is thin and tranfparent. Some 

 days before caterpillars change into the chryfalis ftate, they 

 void, along with their excrement, the inner tube which 

 lined their ftomach and inteftines. When about to pafs in- 

 to the chryfalis ftate, which is a ftate of imbecility, caterpil- 

 lars fele£l the moft proper places and modes of concealing 

 themfelves from their enemies. Some, as the filk-worm, 

 and many others, fpin filken webs or cods round their 

 bodies, which completely difguife the animal form. Others 

 leave the plants upon which they formerly fed and hide 

 themfelves in the little cells which they make in the earth. 

 The rat -tailed worm abandons the water upon the approach 

 of its metamorphofis, retires under the earth, where it is 

 changed into a chryfalis, and, after a certain time, burfts 



