REASONS WHY THE SPECIES IS SINGLE-BROODED. 243 



ited eggs and left June 7. On July 8, the young hatched and were 

 thick, but they did l}ut little damage^ and soon left^ no one Jcneiv whither. We 

 have a similar statement from Professor Aughey. In 1865, the insects 

 which hatched in Dakota County, Northeastern Nebraska, did not leave. 

 They laid eggs which hatched the same season, and the young all per- 

 ished. 



We have also most conclusive evidence from Mr. E. B. Soper, of 

 Esterville, Emmett County, Iowa, of the second brood in 1873 coming 

 to naught. His account, as that of a resident, has weight, and accords 

 with history. He writes us that the locusts came from the southwest 

 in June, about the 23d ; they did much damage ; laid in July, scattered 

 and passed on, some, however, remaining. Many of the young hatched 

 through the autumn and perished, but the bulk of them did not hatch 

 till the spring of 1874, from the last of April to the middle of May, 

 when the greatest damage was done. Mr. G. F. Blanchard, of Fremont, 

 Nebr., (Ai)p. 8), also records the insects that came there from Texas in 

 June, 1873, as laying eggs. The eggs hatched, but no further account 

 is given of the young. 



While, therefore, we admit the possibility of a second generation, we 

 believe that it is exceptional, and that the insects composing such sec- 

 ond generation seldom, if ever, attain maturity or perpetuate their kind. 

 That the species is essentially single-brooded, will appear from the fol- 

 lowing generalizations : 



1st. It is sub-boreal in range and comes to perfection only where the 

 winters are long and severe and the summers short. 



2d. In years of disastrous invasion from the northwest, in late summer 

 and autumn, the insects have not prevailed to the south during the 

 spring. 



3d. In years when the insects hatch and prevail in the Temporary 

 region, the exodus therefrom in early summer is virtually complete, and 

 there are no disastrous incoming swarms into the same region later in 

 the season. 



4th. Where the species has been observed to breed, as in Minnesota 

 and northerly regions, for two or three consecutive years, but one annual 

 generation is produced. 



5th. The insects which reach Manitoba in June and July from the 

 south lay, but the bulk of the eggs remain unhatched till the following 

 spring. The same holds true in Minnesota, for the records show that 

 the eggs laid in June and July, 1873, mostly remained unhatched till 

 1874. 



Single-broodedness is, then, the rule. Like all rules, it has its excep- 

 tions. Many insects that are monogoneutic in northerly latitudes 

 become digoneutic farther south ; yet most of the locusts that we have 

 studied, are monogoneutic even in the latitude of Saint Louis. Galop- 

 tenus atlanis, the nearest allied to spretus, is one of the exceptions, for 

 we have proved it to be double-brooded, This fact indicates that if 



