12 BEES AND WASPS [OH. 



constructing a neat and sharply defined entrance 

 somewhat simpler. 



To return to the individual we have followed : a 

 careful sifting of the sand yielded two paralysed 

 spiders, each with one egg laid upon it and fastened 

 in exactly the same place, viz. on the front end of 

 the upper side of the spider's abdomen and slightly 

 to the right of the middle line. I suspect that even 

 if the spider recovers from the effects of the sting- 

 it is unable to detach the egg, or grub resulting 

 therefrom, from this position. Numerous exhuma- 

 tions of spiders always brought to light the same 

 species (Lycosa picta) and always with the wasp's 

 egg or grub in the same inaccessible position. The 

 constancy of this one species of spider as the object 

 of the attentions of P. plumbeus raises the question 

 by what sense, that of sight or of smell, does the 

 wasp find and follow her prey? The behaviour of 

 the wasp when actually on the trail certainly points 

 to her following a scent; her movements instantly 

 recall those of a hound, while the quick quivering 

 touch of her antennae upon the ground suggests 

 that she is gaining information by these, her olfactory 

 organs. On the other hand it is noteworthy that of 

 the two spiders which alone were abundant upon the 

 sand-dunes, Lycosa picta is by far the more con- 

 spicuous, being of a dark grey colour with a few 

 black markings, which show up plainly, especially 



