66 
The May-flies and Stone-flies 
fall to 
the water’s surface and there are swept along by wind and wave, 
until finally cast up in thick winrows, miles long, 
on the lake beach. Millions of dead May-flies 
are thus piled up on the shores of the Great 
Lakes. 
We call the May-flies the Ephemerida, after 
the Ephemerides of Grecian mythology, and the 
name truly expresses their brief existence—above 
water. But they have lived for a year at least 
before this, or for two or even three^y^ars, as 
wingless, aquatic creatures, clinging concealed 
to the under side of stones in the lake or stream 
bottom, or actively crawling about after their food, 
which consists of minute aquatic plants and animals 
or bits of dead organic matter. In this stage their 
whole environment, habits, and general appearance are 
radically different from those of the brief adult life. We 
can only guess, if our curiosity compels us to attempt some 
explanation, at the manner and the cause of such a 
strange life-history. What advantage is there in such a 
specialized condition that Nature could not have arrived 
at by less indirect means ? What is indeed the utility of 
the whole modification? The quick answer “utility,” 
which is to account for all such strange structural and 
physiological conditions on the basis of useful adapta¬ 
tions brought about by the slow but persistent action 
of natural selection, leaves us, confessedly, answered 
simply on a basis of belief. In hundreds of cases that 
may come under our observation, in how few are we 
really able to perceive a reason-satisfying course of adap¬ 
tive development based on the selection of useful small 
fluctuating variations ? 
The eggs of the May-fly fall from the body of the 
mother to the water’s surface in two packets, which, 
Jj however, break up while sinking, so that the released 
Fig. ioi. —May-flies about an electric lamp. 
