( 4a) [xxiv-xxv 
where, and Ammophila hirsuta flying ina swarm. The latter 
it will be remembered was found by Fabre in hundreds under 
a flat stone on the summit of Mont Ventous, on a cold rainy 
day. Fabre had suggested that the insects were perhaps 
migrating from one district to another, and had paused to rest 
on the mountain-top; but the observation on Pefialara threw 
new light on the interpretation ; for these Fossors as well as 
the Dorcadion were in a state of great activity in the bright 
sun and were pairing freely. Furthermore, both were in 
fresh condition and had evidently only recently emerged from 
the pupal state. ; 
It was suggested as probable that certain species of insects 
with powerful flight, after reaching the imaginal state, have 
the instinct to seek conspicuous isolated features in the 
landscape, that in others with smaller powers or unable to fly 
the instinct is merely to ascend. The effect of both tendencies 
is to reduce the area over which the sexes have to find each other. 
A somewhat deferred maturity and the gradual collection of 
scattered individuals into swarms is probably associated with 
the instinct in many cases, facilitating still further the meeting 
of the sexes and the pairing of individuals from remote areas. 
It is obvious that the gathering swarm will be far more easily 
seen than single insects by the scattered individuals around. 
The swarming of beetles, etc., round tree-tops is probably to be 
thus explained. Related to the same combination of instincts 
preparatory to pairing is the driving off of the winged males 
and females by the workers of ant communities in response to 
some probably atmospheric stimulus which makes itself felt on 
a single day over a vast area. In the case of Lasius niger at El 
Escorial in July, 1902, the President had observed the workers 
driving off the males and females in separate waves, thus 
rendering it more probable that each would mature in the 
presence of the opposite sex from other formicaria rather 
than from their own. 
In the discussion which followed on the tendency of insects 
to seek high and exposed places, Dr. T. A. CHapmMan suggested 
that whereas it is necessary that hybernation should be as 
complete as possible, hill-tops and similar situations would be 
affected as places where the cold would be continuous. Com- 
