628 KEPORT UNITED STATES GEOLOGICAL SURVEY. 



strated tne fact that a temperature of 2^ degrees below zero was fatal 

 to them. 



The embryos evidently get tbeir growth in the antumn and lie dor- 

 mant until the spring before hatching. Mr. Whitman writes me under 

 date of February 3, 1877, from Saint Paul, Minn., " We are inter- 

 ested here to know how near the eggs can reach hatching and still 

 remain uninjured by feezing, and I have some eggs that were just taken 

 from ground frozen solid, and were hatched after being kept moist and 

 warm tliree days. I heard yesterday of a gentleman who started for 

 Chicago with some eggs in his pocket and found them hatched on reach- 

 ing that place." 



In Missouri, the eggs mostly hatch in the middle of April and early in 

 May, while some continue to hatch until June 1. The young acquire 

 their wings in about seven weeks. — (Riley.) 



In Kansas, the eggs hatched the first week in April, and the young 

 first became winged May 28 and 29, and began to fly away then, until 

 June 22. 



The locusts leave Kansas, Nebraska, and Missouri about the middle 

 of June, and are said to fly in a general northwestward course, while the 

 fresh broods from the Rocky Mountains enter these States from about 

 July 20 until the middle or last of September. 



In Nebraska, they were fledged in 1874, about the 7th of June, and 

 then began to fly away, and by the 6th of July they had about left the 

 State. These dates will approximately apply to Minnesota and Iowa for 

 the swarms from the Rocky Mountain region. In Iowa the grass- 

 hoppers in 1874 entered the State from the south and west about the 

 10th of June; these were the swarms from Kansas, or " probably deflected 

 from their usual course by adverse winds." In Minnesota the young 

 hatch in April and May, and get their wings and btgin to depart about 

 July 1, the departure becomiug general about the 10th, and total by the 

 end of August. 



In Colorado, on the ])lains at the elevation of Denver, the eggs begin 

 sometimes to hatch in March and continue doing so until early in May. 

 The locusts acquire their wiugs and fly ofl" about the first or middle of 

 June. The swarms from the north and westward appear about the 20th 

 of July, and continue to arrive until early in September. Among the 

 foot-hills the eggs hatch in May, and at an elevation of 8,000 or 9,000 

 feet in June and even July the young in the subalpiue elevations among 

 the mountains in may cases perishing from the cold before acquiring 

 wings. In Dakota, in 1874, they became winged during the first week 

 in June and disappeared by the middle of July. 



It is not generally known that the great powers of flight in the grass- 

 hopper as well as most other winged insects is due in part to the pres- 

 ence of large air-sacs. These sacs are expansions of the air-tubes 

 which ramify throughout the interior of the body. They are found in 

 the head and thorax, but are largest (especially in the honey-bee) in the 

 base of the hind body. They do not occur in insects which simply 

 crawl or walk. In the grasshoppers {Acrydii)^ most of the transverse 

 anastomosing tracheae iu the abdomen have large air reservoirs, greatly 

 assisting in lightening the body and sustaining it in their long flights. 

 It is from their development, probably, in the western locust (I have 

 found them well developed in several eastern allied forms) that this in- 

 sect is enabled to sail so lightly and easily for hours at a time in the air 

 hundreds or even thousands of feet above the ground, as well as to 

 spend days, perhaps, iu its long flights during the migratory season. 



The following valuable notes on the natural history of the grasshop- 



