474 INSTINCT OF INSECTS. 



could not sew together the membranes composing it at 

 the inner side, without cutting them in part from the leaf. 

 While, therefore, they divide the major part of their in- 

 ner side from the leaf, they artfully leave them attached 

 to it by one of the large nerves at each end : and these 

 supports they do not cut asunder until the intermediate 

 space has been sewed up, and they are ready to step, 

 with their house on their back, upon the terra Jtrma of 

 the disk of the leaf. In this instance, therefore, the 

 larvae do not wholly separate their case from the leaf, 

 until it is sewed. But when the same larvae cut out their 

 materials from the middle of the leaf, where, though com- 

 pletely cut round, they are retained in their situation se- 

 cure from all danger of falling by the serratures of the 

 incisions made by the jaws of the larvae, these little 

 tailors vary their mode, and entirely detach the pieces 

 from the surrounding leaf, before they proceed to set a 

 stitch into them a . 



In the preceding instances the variation of instinct 

 takes place in the same individual, but Bonnet mentions 

 a very curious fact in which it occurs in different genera- 

 tions of the same species. There are annually, he in- 

 forms us, two generations of the Angoumois moth, an 

 insect which has been before mentioned b , as destructive 

 to wheat : the first appear in May and June, and lay 

 their eggs upon the ears of wheat in the fields ; the se- 

 cond appear at the end of the summer or in autumn, and 

 these lay their eggs upon wheat in the granaries. These 

 last pass the winter in the state of larvae, from which 

 proceeds the first generation of moths. But what is ex- 



a Reaum. Hi. 112-119. " VOL. I. 172. 



