THE MICROCOSM OF THE DRIFT LINE. 
LAETITIA M. SNOW. 
IN the spring of 1902 my attention was called to the 
extremely interesting life relations of insects along and 
around the line of drift thrown up by the waters of Lake 
Michigan, and a series of collections and observations were 
made between April 14 and May 31. The collections included 
one hundred and fourteen species, only fifty-one of which it 
was possible, with the means at hand, to identify. The speci- 
mens have, however, been preserved. 
PuvsicaL FEATURES. 
As with life everywhere, the physical features of the habitat 
are of great importance to the population. For instance, on 
Windsor Park beach, including the region north to Seventy- 
Second Street and south to the Steel Works, the forms were, 
as a rule, much more abundant than on the two beaches in 
Jackson Park. On the former beach the gradient is low and 
the sand smooth ; the water action is rather gentle, the insects 
stay when the water retreats, and the fine sand keeps them 
on the surface. At Jackson Park beaches, on the other hand, 
unless the water has recently been high and beyond the pebble 
zone, the collecting is poor. In the pebble zone the gradient 
is greater, the water action greater, and there is the possi- 
bility of the insects being washed out again into the lake. 
That the physical conditions of the beach account for the 
greater number of forms, and not the fact that collections at 
the two places were made at different times, may be proved 
by the fact that on the same day a pebble region of beach 
north of Windsor Park gave no results, while a smooth region 
yielded a number of forms. 
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