No. 431.] MICROCOSM OF THE DRIFT LINE. 861 
an unknown impulse to take a common migration. Riley (5) 
makes the statement that “all insects acquire the migratory 
instinct when crowded together through excessive multiplica- 
tion." The probable response to meteorological influences has 
been noted. 
Hancock (9) distinguishes between dispersal and migration 
in the statement, * Individuals of a species which effect a 
more or less regular periodical change in their habitat are 
truly migratory. Migrations may be primary, consisting of 
local flights, such as movements by insects hatched in tem- 
porary regions, to which they confine themselves to passing 
to and fro, from point to point; or secondary, as the repeated 
periodical changes of residence covering foreign fields, which 
naturally establishes a nomadic habit." In addition to these 
distinctions it is suggested that the term “migrations” be 
confined to periodical changes of habitat resulting from the 
normal sequence of temperature and season, while such abnor- 
mal occurrences as the devastating swarms of Rocky Moun- 
tain locusts or irregular and unusual swarms, as in certain 
instances of butterfly, moth, and dragon-fly flights, be given, 
temporarily at least, the term “immigration.” Mr. Hancock's 
*primary migrations or local flights" would be simply dis- 
persal flights of individuals or groups of individuals within 
their area of distribution. 
Was the flight of Colorado potato beetles on May 27 a dis- 
persal (or local) flight, diverted out of its course and driven 
lakeward by west winds, or was it a periodic migration? The 
predominance of other insects at various times was probably 
due to the spreading of groups of individuals by local flights : 
may not these local flights give some evidence of the dispersal 
paths of various species ? 
CONCLUSION. 
By whatever means the animals reached the region, — by 
migration or dispersal movement, — the life relations of the 
beach are not altered. We have here a little community of 
food providers and food obtainers, whose population varies 
with the season, the wind (probably), the beach conditions, 
