312 PROCEEDINGS OF THE ACADEMY OF [June, 



Suppose a different experiment were performed : let some muskrats 



i Fiber) be put into an aquarium with some sea-lions ; would their 



•efforts to escape indicate previous experience in evading enemies of 



-the same class? Not at all, it would indicate merely adaptation to 



expert progression in the same medium. The relations of birds 



(in general) to bats and of birds (again in general) to dragonflies are 



instances illustrating the same fact, but which are due to no general 



predatory relation between the groups. The wonderful powers of 



flight of many of the Syrphida? are strictly comparable to that of 



butterflies, as the adults feed only at flowers and have no need of 



expert flight for predatory purposes; also they do not need it so 



highly developed for defense, for rather a small proportion of birds 



are capable of catching insects so expert on the wing. The extreme 



rapidity and dexterity of flight of humming-birds has no possible 



relation to their prey, nor need it have been developed to its present 



perfection to evade species that might be inclined to prey upon 



hummers. When Mr. Pocock arrives at the true reason for the 



extraordinary powers of flight of humming-birds, he will undoubtedly 



be less insistent upon the predator-evasion theory as an explanation 



of the tortuous flight of butterflies. 58 



Pocock further says: "Those who hold on the negative evidence 

 above stated, that birds are not to be reckoned as serious enemies 

 of butterflies, must be called upon to supply some explanation other 

 than that above proposed of the marked reactions between these 

 two classes of animals when brought into contact with one another, 

 and to show reason why what takes place in the aviary may not be 

 regarded as indicative of similar occurrences in nature" (p. 812). 



The pertinent retort to this statement is that it is the selectionists 

 who first claimed and who still claim that birds are important enemies 

 of butterflies, and it is up to them to produce real evidence in favor 

 of their contention. So far they have brought forward little except 

 results of experiments. Pocock's own results, namely, the consump- 

 tion of large numbers of British insects by exotic animals, should 

 have convinced him that what takes place in the aviary may not 

 necessarily be regarded as indicative of similar occurrences in nature. 

 The point may be further illustrated by the following. Suppose a 



5S It is a matter of common observation that butterflies constantly exercise 

 their powers of flight by playing with other butterflies even of different species. 

 They often dart at falling leaves, flying bits of paper, and even birds. The 

 writer saw (March 27, 1912, Plummer's Id., Md.) a Vanessa antiopa dash at 

 and come within a few inches of a phcebe (Sayornis), that had just perched after 

 •one of its customary quick sallies at insect prey. The bird, a highly insectiv- 

 orous species, paid no attention to the butterfly. 



