3o4 Mr. G. A. K. Marshall on Birds as a Factor in the 



happen to force themselves on the collector's attention ; 

 the collector must resolutely set himself to search out and 

 keep watch upon Avhat really takes place. Seeing that 

 there is no record of any naturalist's having seriously taken 

 up the investigation of this matter in the field, I think 

 that very much positive evidence could hardly be ex- 

 pected, and that what has been published goes far in the 

 direction of proving that birds must still be reckoned 

 among the principal enemies of butterflies," We must 

 likewise bear in mind that ex hypothcsi we may expect the 

 attacks of birds to be comparatively infrequent in all 

 those places where mimetic resemblances among butter- 

 flies are rare or absent. It is in the region of tropical 

 forests, where both birds and insects are plentiful, tliat 

 this phenomenon attains its greatest frequency and its 

 highest perfection ; but it is precisely in such localities 

 that adequate observations are most lacking. The few 

 entomologists who visit these favoured spots are, not 

 unnaturally, too much preoccupied in the task of mere 

 collecting to be able to devote themselves to long and 

 possibly tedious observations of this kind. And only 

 those who have actually tried it can realise how much 

 time and patience is requisite to obtain even small results, 

 unless the conditions for observation are very exceptionally 

 favourable. Still there can be little doubt that in suitable 

 localities even the busiest collector might add at least a 

 few crumbs to our store of knowledge if he would but keep 

 his eyes open for such occurrences and carefully note the 

 details at the time. In this connection I may quote the 

 remarks of that excellent observer. Dr. Franz Doflein, of 

 the Munich University, who, in his interesting book on his 

 travels in the East, has made some valuable contribu- 

 tions to the present subject (" Ostasienfahrt," 1906, pp. 

 440-446). He there says : " From the observations which 

 I made in the jungles of Ceylon it is quite incom- 

 prehensible to me how naturalists who have spent years 

 and tens of years in the tropics can deny this fact [that 

 butterflies are frequently attacked by birds]. I can 

 only suppose that during their wanderings they pay no 

 special attention to such occurrences, so that when on their 

 return they take part in theoretical discussions, they 

 search their memories and their note-books in vain for 

 records of such observations." 



As an instance of the manner in which such facts 



