422 TOWER, DARWINISM. 
In these locations unaltered natural conditions prevailed. The 
butterflies were abundant and their enemies were present in the 
strength nature provided, so that whatever elimination took place 
was the result of the struggle for existence in the forest and was 
not due to anything that I introduced. On each visit to these 
locations, the area was marked off with white cord stretched 
between the posts and further subdivided into plots two metres 
square. With a force of keen-eyed natives, each plot was gune 
over inch by inch and all of the wings of all the Lepidoptera that 
were found were gathered for examination. 
It is well known that predacious enemies, as a rule, do not 
devour the wings of Lepidopterous insects, but these are bitten 
off and dropped. It is found that Lepidopterous insects killed by 
birds show a relatively clean cut across the base of the wing when 
the wing is severed from the butterfly’s body by a bird’s beak. 
Those killed by ants have a portion of the body wall adhering to 
the base of the wing, as do those killed by spiders, in which case 
a considerable portion of the body often remains. It is relatively 
easy to distinguish the wings of Lepidoptera killed by birds or by 
vertebrate enemies from the wings of those killed by predacious 
invertebrates. For convenience we may divide the findings into 
two classes or into eliminations due to vertebrate and inverte- 
brate enemies. Vertebrate enemies are assumed by Natural Selec- 
tionists to exercise discrimination, but I know of no instance in 
which this discrimination has been attributed to ants, dragon-flies 
and spiders. 





The wings of the Lepidoptera recovered were sorted out andin 
this sorting every doubtful instance was attributed to the vertebrate 
enemies, so that the efficiency of the enemies supposedly possessing 
discrimination and capable of the selective cffect was given the 
benefit of every doubtful case. As an added precaution that no 
wings should be missed and to guard against any discrimination 
on the part of my searchers, due to their finding out exactly what 
types were of most interest to me, they were paid one centavo 
for every ten pairs of wings found, so that the more wings, the - 
more money. 

