HABITS NOT INVARIABLE. 245 



propolir, . . . and there could be no doubt of their 

 having been guided by reason." Such cases have, how- 

 ever, been observed. Andrew Knight found that his 

 bees collected some wax and turpentine with which he 

 had covered some decorticated trees, and used it instead 

 of propolis, the manufacture of which they discontinued. 

 Nay, M. Fabre has himself placed on record some cases 

 of the same kind, and shown that the instincts of these 

 animals are not absolutely unalterable. Thus one 

 solitary wasp, Si:)liex flaviioennis, which provisions its nest 

 with small grasshoppers, when it returns to the cell, 

 leaves the victim outside, and goes down for a moment 

 to see that all is right. During her absence M. Fabre 

 moved the grasshopper a little. Out came the Sphex, 

 soon found her victim, dragged it to the mouth of the 

 cell, and left it as before. Again and again M. Fabre 

 moved the grasshopper, but every time the Sphex did 

 exactly the same thing, until M. Fabre was tired out. 

 All the insects of this colony had the same curious 

 habit; but on trying the same experiment with a 

 Sphex of the following year, after two or three dis- 

 appointments she learned wisdom by experience, and 

 carried the grasshopper directly down into the cell. 



Eumenes fomiformis builds, as already mentioned, 

 a cell in the open air. If attached to a broad base, 

 *' C'est un dome avec goulot central, evase en embou- 

 chure d'urne. Mais quand I'appui se reduit a un point, 

 sur un rameau d'arbuste par exemple, le nid devient 

 une capsule spherique, surmontee tonjours d'un goulot, 

 bien entendu." * 



Again, he has shown good reason for believing 

 that, although the Tachjtes nigra generally makes its 

 * Loc cit, p. 66. 



