HABITS NOT INVARIABLE. 245 



propolis, . . . and there conld 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 propob's, the manufacture of which they discontinued. 

 Na}', M. Fabre has himself placed on record some cases 

 of the same Itind, and showa that the instincts of these 

 animals are not absolutely unalterable. Thus one 

 solitary wasp, Sphex flavipennis, 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. Eabre 

 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 

 exa'tly the same thing, until M. Fabre was tired out. 

 All the insects of this colony had the same curious 

 lialdt; 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 pomiformis 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 dt vient 

 une capsule spherique, surmontee toujours d'un gonlot, 

 bien entendu." * 



Again, he has shown good reason for believing 

 that, although the Tachytes nigra generally makes its 



* Loc, eit., p. 66. 



