Origin and Diffusion on ft/issus leucopterus and Murgantia histrionica. 149 



that is the quite general preference shown by the females in selecting 

 any slight elevations in the fields, such as hummocks or even what are 

 known in agricultural parlance as "back furrows," where two furrows 

 are thrown together forming a slight ridge, as places for ovipositing: 

 and I have noticed in large fields of comparatively low, flat land, that 

 the wheat on these slight elevations would turn white and die from 

 attack while the lowest portions would remain uninjured ; precisely as 

 if the females had expected to avoid all probability of their progeny 

 being submerged by a sudden, excessive rain fall, tides, or unusually 

 high waves, such as would be likely to occur in a tropical country or 

 along the sea shore. It seems to me that we may here have another 

 illustration of an ancient habit, formerly followed throughout a long 

 period of time, through necessity, and now by inherited instinct. 



Mr. Schwarz has cited the extreme susceptibility of Blissus leuco- 

 pterus to the influence of moist weather, as being in striking contrast 

 with the behavior of other insects which are native to the states in- 

 habited by it in North America, and thinks that this, with the fact 

 that it seems almost wholly free from parasites, points strongly to its 

 being an immigrant from some other more or less distant habitat. I 

 would not only coincide in this opinion, but beg permission to add 

 three other, so far as I can see, equally strong points. Lack of varia- 

 tion from the type, would indicate a strict adherence to old established 

 habits, or a short residence in North America, while the frequent oc- 

 currence of adults with aborted wings would imply that it had, some- 

 time, lived where either the wings were useless or else their use would 

 render the possessor liable to be blown out to sea. Darwin in "Jour- 

 nal of Researches " has called attention to the probability of insular 

 insects either being provided with especially strong wings, or none at 

 all, in order to protect them from being carried away by the wind. 

 This, of course, does not apply to such species as are apterous in one 

 generation and winged in the other, like Isosoma tritici, or where the 

 female alone is apterous, as in Anisopteryx and Orgyia, in Lepidoptera, 

 and Tyloder?na fragarice, in Coleoptera. It is easy to see that a species 

 as migratory as the chinch bug, if inhabiting a narrow tract of land 

 swept by cross winds, would have need of such a protection, and, in 

 fact, Mr. Schwarz finds it apterous along the east coast of Florida, so 

 that we here have an occasionally appearing character that may, in- 

 land, be the remnant of an ancient condition. That Blissus leuco- 

 pterus is only very slightly variable is quite in harmony with the whole 



