﻿OP THE STATE ENTOMOLOGIST. 153 



Red-legged, the Atlantic and the Diiferential locusts: in no instance 

 was a specimen of sprehis seen. The several specimens obtained 

 from Ford county were all Atlanis; a single specimen received from 

 Mr. H. J. Dunlap, of Champaign, was a male femur ruhrum^ while 

 specimens taken by Prof. Biirrill, of the Industrial University, at the 

 same place, as well as others from Norwood, Mercer county, sent to 

 Prof. Thomas, were diiferentialis. The parties capturing these speci- 

 mens are not apt to fall into error, and are all positive that the speci- 

 mens submitted were from the flying bevies. 



From these facts it results that two species, viz : femur-rubrum 

 and diiferentialis^ihovigh. normally having no migratory habit, and, as 

 I believe, incapable of extended flights, can actually assist in such 

 flights. That the bulk of these Illinois swarms was composed, how- 

 ever, of Atla7iis, scarcely admits of a doubt. The other two, less able 

 to sustain lengthened flight, would naturally be most near the ground 

 and most often captured ; while Atlanis^ which we now know to occur 

 in this part of the country as well as East, and to often display the 

 migratory habit, would fly higher. 



There are two facts which it will be well to bear in mind in this 

 connection, as explaining the above phenomena. The first is that, as 

 we have already seen, Atla7iis was very common in Missouri, even in 

 fields where it had never been noticed before. It prevailed to such 

 an extent in Illinois, that around Carbondale, Prof. Thomas could not 

 find a single specimen of the typical feinur-ruhrum^ and there was 

 not a single sjjecimen of it among a number which he caused to be 

 collected for me. So obvious was this fact that Prof. Thomas was led 

 to suggest in the Chicago Inter- Ocean of October 9, 1875, that the one 

 was the out-growth of the other. I quote his language : 



This species [femur-rubrum) whicii can usually be found anywhere in the fields or 

 alono^ the roadside during the Summer and Fall, appears to be entirely replaced by a 

 new form, Avhich I take "to be the one described by Prof. Riley as Caloptenus Atlanis 

 whicli is an intermediate form between V, femur-rubrum and C. spretus, so near, in fact, to 

 the latter that it is almost impossible to distinguish the one from the other. 1 have 

 searched in vain for femur rubrwn, it seems to have entirely disappeared, and that the 

 new variety has taken its place. Is the one the progenitor of the other : the former of 

 the latter? 1 am no believer in Darwinianism, but here is presented a problem difficult 

 to solve, unless we admit the correctness of that theory, or, that all three supposed 

 species are but varieties of one, which I am half-way inclined to believe is the case. 

 Otherwise how are we to account for the appearance of this new form this season? 

 The spretus has not visited our section, the femur-rubrum is absent, and here I have be- 

 fore me a large number of specimens gathered here, some of them to-day, with the 

 long wings and the notched male abdomen, corresponding exactly to Professor Riley's 

 description of Caloptenus Atlanis? Is the common femur rubrum being transformed 

 into spretus^ this being the intermediate step? If so, over half the distance has al- 

 ready been traversed. 



The second factis, that ^/^f^rtjniJmZ?'^ was also unusually abundant. 

 A letter from Mr. M. BrinkerhofF, of Onarga, Illinois, dated October 18^ 



