280 BULLETIN OF THE BUREAU OF FISHERIES. 
most abundant) and 25, and August 16; nymphs collected by Dr. A. D. Howard from the 
stream bed of Andalusia Chute just above Fairport, showing 12 occurrences in 102 col- 
lections; fragments of hundreds of adults (mostly females) from the full stomachs of 
the river herring, Pomolobus chrysochloris, sent by Director Shira. With these were a 
few nymphs that were probably taken when on their way to the surface to transform; 
and many nymphs taken from the stomachs of the shovelfish, Polyodon spathula, at Lake 
Pepin, and sent me by Dr. George Wagner, of the University of Wisconsin. These were 
doubtless taken while on their way to the surface, for they were eaten just before the 
swarms of adults appeared and at no other times (Wagner, 1908). The particular speci- 
mens sent me bear date of June 21, 1904. 
Other material made up of that collected by Prof. J. H. Comstock at Peoria, IIl., 
on July 17, 1887, and at Kidders Ferry on Cayuga Lake, N. Y., on July 17, 1886; by 
Prof. T. L. Hankinson at Walnut Lake, Mich., in June and July, 1906; by Prof. C. 
Betten at Buffalo, N. Y., on the 18th, the 24th, and the 31st of July, 1906, and in Storm 
Lake, Iowa, in June, 1902; by Prof. C. C. Adams at Ann Arbor, Mich., in June, July, and 
August, 1904; by Prof. George D. Shafer at Lansing, Mich., on August 16, 1906; by 
E. B. Williamson at Howe, Ind., on September 14, 1916; by Prof. C. R. Crosby at Co- 
lumbia, Mo., on June 16, 1905; and by myself in Lake Michigan, at Lake Forest, IIl., 
Walnut Lake, Mich., and Cayuga Lake, Ithaca, N. Y., July and August of several years. 
Hapits.—This species, though found in a wide variety of situations, prefers shoal 
waters whose beds are covered with soft ooze, rich in organic materials. There the 
burrowing is easy and food is abundant. Figure 2 of Plate LXX shows a soft-mud bank 
left bare by the receding stream. A portion of the mud has fallen into an undercutting 
current, and in the portion that remains undisturbed a section is exposed, perforated in 
all directions by the many burrows of the Hexagenia nymphs. Miss Morgan (1913, p. 99) 
has thus described the burrowing of the upland species which she studied: 
The sloping banks were mined by Hexagenia nymphs, the open burrows showing only 2 or 3 inches 
apart. Most of the burrows were apparent by their round openings; from some, hairy caudal sete pro- 
truded at full length. When a nymph was pulled out it speedily began to burrow again, placing the 
fore legs together with the bladelike tarsi held vertically. It next pressed them forward and outward, 
at the same time wedging the head between them in the cavity thus made. This movement was followed 
by a sudden lurch of the body forward, accompanied by wriggling of the abdomen. During these mo- 
tions the second pair of legs was folded close up to the body, while the third pair was held outstretched, 
ready to brace against the mud. These motions, rapidly repeated, enabled the nymph to bury itself in 
a surprisingly shorttime. Some of thesoft ooze taken from where the burrows were most numerous 
was later examined in the laboratory and found to be packed with diatoms. Stomachs of two of the 
nymphs were found full of silt and diatoms, showing that the nymphs had found plentiful forage as they 
burrowed. 
The length of nymphal life is unknown, possibly two years, if one may judge by the 
half-grown nymphs one finds in midsummer. ‘Transformation occurs at the surface of 
the water and usually at night. The grown nymph swims up and floats. A rent appears 
in the skin of its back. The subimago suddenly emerges from this rent, its wings ex- 
panding full size almost instantly. It stands a moment on the surface and then rises 
and flies away to the shore. It settles on any convenient support, often alongside 
countless others of its kind, as figure 1 of Plate LXX testifies, and remains quiescent 
for about 24 hours, when it molts again and becomes fully adult. Probably on the even- 
ing of the day following its final molt (I do not know that this has been determined in 
