Another Prober 



species, which is recognized as large or small 

 from the outward aspect of its house. I re- 

 fuse to go to this length in my conjectures, 

 not that instinct seems to me incapable of such 

 feats, but because of the particulars obtained 

 from the Three-horned Osmia and the two 

 Mason-bees. 



In the cells of these three species, I see the 

 number of larvae put out to nurse vary in so 

 elastic a fashion that I must abandon all idea 

 of proportionate adjustment. The mother, 

 without troubling unduly whether there be an 

 excess or a dearth of provisions for her 

 family, has filled the cells as her fancy 

 prompted, or rather according to the number 

 of ripe ovules contained in her ovaries at the 

 time of the laying. If food be overplentiful, 

 the brood will be all the better for it and will 

 grow bigger and stronger; if food be scarce, 

 the famished youngsters will not die, but will 

 remain smaller. Indeed, with both the larva 

 and the full-grown insect, I have often ob- 

 served a difference in size which varies ac- 

 cording to the density of the population, the 

 members of a small colony being double the 

 size of their overcrowded neighbours. 



The grubs are white, tapering at both ends, 

 sharply segmented and covered all over their 



71 



