398 FOOD OF INJECTS. 



— a power of stomach which our graziers may thank 

 their stars that their oxen are not endowed with. A 

 probable proximate cause for this voracity in the case 

 of herbivorous larvae has been assigned by John Hun- 

 ter, who attributes it to the circumstance of their sto- 

 mach not having the power of dissolving the vegetable 

 matters received into it, but merely of extracting fronj 

 them a juice*. This is proved both by their excre- 

 ment, which consists of coiled-up and hardened parti- 

 cles of leaf, that being put into water expand like tea; 

 and by the great proportion which the excrement bears 

 to the quantity of food consumed. From experiments, 

 with a detail of which he has favoured me, made by Colo- 

 nel Machell on the caterpillars o? Bombt/x Caja, he as- 

 certained that, though a larva weighing thirty-six grains 

 voided every twelve hours from fifteen to eighteen 

 grains weight of excrement, it did not increase in 

 weight in the same period more than one or two grains. 

 On the other hand, many carnivorous larvai increase in 

 weight iu full proportion to the food consumed, and that 

 in an astonishing degree. Redi found that the mag- 

 gots of flesli-flies, of which one day, twenty-five or 

 thirty did not weigh above a grain, the next weighed 

 seven grains each; having thus in twenty-four hours 

 become about two hundred times heavier than before ''. 

 Some insects have the faculty of sustaining a long 

 abstinence from all kinds of food. This seems to de- 

 pend upon the nature of their habits. If the insect 

 feeds on a substance of a deficiency of which there is 

 not much probability, as on vegetables, &c., it com- 



* Obs. on the Animal CP.vonom'j^ p. 221. Compare Reaum. ii. 161 . 

 > Redi (7e Insedh,'^^. 



