210 



range of these species, lu clear weather the temperature over 

 the blow-sand is probably higher by day and lower at night 

 than in the case of ordinary soil, but the difference in this 

 respect can not be great between some grassy tops of sand-hills 

 occupied hj f{ari(hit< and a close-cropped prairie pasture where 

 friinir-nihniiii abounds. With regard to the sparseness of the 

 vegetation usual on sand-dune tops, this can hardly be an influ- 

 ential factor, as it is not a constant feature of the areas known 

 to be occupied by fin rid hs; and the mechanical effect of drift- 

 ing or loose sand upon such active insects with so well-devel- 

 oped an exoskeleton, is surely of little consequence to them. As 

 to protective coloration, both of these species are protectively 

 colored. McNeill ('91) notes the strongly imitative colora- 

 tion oifiavidiis on sand; fciinir-nthniiii is slightly darker above 

 than Jidvidiis, and therefore better suited to an ordinary 

 soil surface; but, in any case, protective coloration is an 

 effect rather than a cause. Insects which are adapted to ob- 

 tain food in exposed situations usually approximate the ap- 

 pearance and color of something in their normal surround- 

 ings, but surely do not ht themselves in wherever their original 

 coloration matches best. The next factor, competition for 

 space, is suggested in explanation of the limitation to sand 

 of insects such a,sjfaridii^, the idea being that they are species 

 also fitted for existence in more favored situations, but simply 

 unable to hold their own there in competition with other spe- 

 cies such as fenuir-nilii'iiDi. The facts of general and local dis- 

 tribution, however, do not support any such idea. Lastly, the 

 effect of sand on the immature stages comes up for considera- 

 tion. This is an important factor, analogous to taking root 

 and dissemination among plants, and may ultimately prove to 

 have a considerable influence on local distribution; but we 

 have no data as to these stages in faciduti. Urasshoppers ordi- 

 narily choose a rather hard soil in which to place their egg mass- 

 es, and excavations in sand are not maintained with the same 

 facility as in earth without special adaptations for the purpose. 

 In general, therefore, it may be said that while there are 

 a number of minor differences in the biotic environment on 



