No. 431.) MICROCOSM OF THE DRIFT LINE. 859 
dead, dying, or active. In the latter case they had in many 
instances crawled up on stones and driftwood, until the sur- 
faces of such articles were, in places, covered with them, some- 
times two layers deep. On May 31, however, very few live 
ones remained, and the total number of individuals was 
greatly diminished. The form that approached the potato 
beetle in number on May 27 was the May beetle, or June bug 
(Lachnosterna sp. ?). 
Besides those above mentioned, other forms occurred in 
greater or less abundance at different times, some running 
through the whole period, some starting late and continuing 
to the end, some starting early and disappearing. 
MIGRATIONS. 
Would the fact that certain forms culminated at certain 
times indicate that they simply reached the adult stage at that 
time, laid their eggs and disappeared, or that they were per- 
forming mass movements, broadly called ** migrations"? The 
great swarm of potato beetles on May 27 closely resembled 
mass movements recorded by many authors, in that the num- 
ber was large and that the animals were found on the 27th 
and by the 31st had almost entirely disappeared, no new ones 
appearing. If it were merely a general emergence, it is not 
likely they would have been found only along the lake front. 
This great washing up of one species recalls the predominance 
of crickets (Memobius fasciatus) described by Needham (1). 
Much has been written on this subject, both descriptive and 
theoretical, but the problems as to the * why " and “ whither ” 
of insect flights have never been solved. The search for food 
has been suggested as the cause, and the suggestion has been 
accepted by many as at least a secondary factor. In some 
cases over-production, followed by a scarcity of food, would 
seem a sufficient reason for the movement ; as, for instance, 
the migrations of locusts, both in this and other countries 
(2, 3). Certain examples of the flights of dragon flies point 
to the same cause (3, p. 509; 4; 10). Kobelt (3) quotes 
Gatke as saying: “Es ist schon darauf hingewiesen worden, 
