


TOWER, DARWINISM. 437 
materials used were uniform, but they differed in the details of 
the several series of observations. 
Elimination in the animals used comes through relations to the 
physical factors of the environment, especially in the water-balance 
relation during the egg-stage, as already pointed out in the case of 
L. panamensis, and in the period of aestivation. The food relation 
is also important, as is the relation of various parasitic enemies, 
more rarely of infectious disease and only very slightly does the 
relation to predacious vertebrate enemies enter into the problem. 
The ‘eliminating processes that take place during the rainy season 
deserve a brief mention, although it is not possible in the scope of this 
paper to present them in any detail. Predacious Hemiptera and egg para- 
rasites eliminate a few in the egg stage, and the same forces eliminate a 
small percentage of the larvae. Pupation in the rainy season is, not, as 
a rule, accompanied by high mortalities, and the freshly emerged adults 
are subjected to only sporadic and trivial eliminating agencies. To 
present adequately the question of elimination in these organisms, it 
would be necessary to consider many aspects in much detail, but the 
general result can be arrived at for the purposes of this paper by 
focussing attention upon an inevitable, annually recurring relationship. 
In all of the tropical areas where I have worked, there is an 
alternation of wet and dry seasons, and in many locations they are 
sharply delimited. The reproductive and growth activities of the 
Chrysomelid beetles are limited to the rainy season, with the dry 
season passed in aestivation. For purposes of observation, [chose 
locations where the two seasons are sharply delimited, rather 
extreme in character, so that with the onset of the dry season all 
of these beetles would go into aestivation within a brief period. 
Well established, isolated habitudinal groups were selected and 
kept under observation for a period of years. These locations were 
visited at appropriate times for purposes of examination and census 
taking, and these censuses gave information concerning a number 
of evolution problems. For this paper, attention is focussed upon 
what happened during the period of aestivation, as it is evident 
that survival of this annual adverse dry period precisely determines 
what the population will be that will take part in the reproduction 
