VALIDITY OF SOME FORMS OF MIMICRY. 743 



The Mullerian Theory. 



The supporters of the Mullerian theory hold the view that it is 

 chiefly by the attacks of the young inexperienced birds that this 

 form of mimiciy is produced. Professor Poulton puts the case 

 as follows : — " The Miillerian theory presupposes that only young 

 birds test the palatability of a few members of each convergent 

 group in their locality and henceforward, except when driven by 

 hunger, avoid all the membei's, so that the recent tendency to 

 explain so man}" of the resemblances on Miillerian rather than 

 on Batesian lines is in harmony with the conclusion that the 

 members of such groups are not greatly attacked by adult birds." 

 (Essays on Evolution, p. 270.) 



I have already expressed the opinion that it is unlikely that 

 young birds, except those in group 1, indulge in tasting experi- 

 ments on butterflies, but as I am quite willing to admit that such 

 an opinion may be founded on insufficient data, and as I was un- 

 able to find the necessaiy evidence required by the Miillerian 

 theory, I approached the subject by another line of investigation, 

 which depends on the time of the nesting of the birds and the 

 broods of the butterflies. 



The birds breed once a year, not twice as is the case in Mauritius. 

 They begin in Mai'ch or April, sometimes early in May, according 

 to the season. When the March or April rains known as the 

 little monsoon bring out a large increase of insect life, the birds 

 immediately begin nesting, and the young birds are off the nest 

 and begin to forage for themselves in May, June or early July. 

 The average life of an insectivorous bird is probabl}^ not more 

 than four or five years, and we may assume that tasting experi- 

 ments gradually grow fewer in number and are completed when 

 the bird is about six months old, i. e. about the month of October. 



In estimating the number of broods of butterflies in the year, 

 which vary much according to the species, I will direct attention 

 to two of the more striking cases of mimicry, that of the Eupkeas, 

 forming a Miillerian combination, and Fapilio polytes with its 

 trimorphic female mimicking P. aristolochice and P. (Menelaides) 

 hector. They may be taken together. In January, February and 

 March, that is to say in the dry weather (I am speaking more 

 particularly of the plains), there is a very small but continuous 

 series of broods which depend on the weather for their develop- 

 ment. If it is very dry, the eggs, larvje or pupse, as the case may 

 be, lie dormant, but with favourable meteorological conditions 

 such as a shower of rain, the eggs hatch, the larvae shake ofi' their 

 lethargy and feed, or the butterfly emerges. Mr. Mackwood in- 

 formed me that on March 24, 1908, in his garden at Colombo, 

 eggs, larvae and pupse of Euploia core could be found together on 

 the same tree. The majority of the pupse do not, however, hatch 

 out but remain quiescent until the April rains, when there is an 

 astonishing outburst of butterfly and other insect life. With the 

 onset of the south-west monsoon at the end of May or beginning 



