600 TRANSACTIONS OF SECTION D. 



FRIDAY, AUGUST 3. 



The following Papers and Report were read : — ] 



1. Some Results of the Infection of Monkeys with Guinea Worm. 

 By Dr. R. T. Leiper. 



2. 



On Epigamic and Aj)osematic Scents in Rhopalocera. 

 By F. A. DixET, M.A., M.D. 



It is well known that the male of Ganoris napi, one of our common white 

 butterflies, exhales a fragrant scent which has been compared to that of lemon 

 verbena, this perfume being probably epigamic in significance. In 1899 and 

 following years the writer detected an odour somewhat similar in character, 

 though not so strong, in the males of certain other British Rhopalocera belonging 

 to the sub-families Pierince, SatyrincB, and LyccBnidce. Wood-Mason (1886) 

 had observed similar phenomena in some Indian species, and Longstaff (1903-5) 

 added several other European and Indian forms to the list. 



During last year's visit of the British Association to South Africa the writer 

 took the opportunity of extending these observations to native African species, 

 very many of which were found to possess an agreeable odour, suggestive in some 

 cases of aromatic vegetable products, such as chocolate or vanilla, and in others 

 of the scents of various flowers. These also were in every case, with one doubtful 

 exception, confined to the male sex. 



In addition to these agreeable perfumes, it has long been recognised that there 

 exists another class of butterfly odours, oftensive in character and probably 

 aposematic in function, being more or less shared by both sexes and generally 

 occurring in forms which are on independent grounds believed to be protected. 

 The writer's impressions as to the scents of either sort were in most instances 

 confirmed in the field by Dr. Longstaff^. 



It might antecedently be expected that both kinds of perfume should in some 

 instances be found co-existing in the same species. Wood-Mason has reported a 

 few such cases from India, and the writer has obtained some evidence that the 

 like condition occurs in Africa. 



There is no doubt that the epigamic scents are in most cases distributed by 

 specialised scales (androconia) or ' hairs ' ; in some forms, however, no special 

 scent-distributing apparatus has been detected. The androconia may be either 

 generally distributed or localised, in the latter case forming the structures known 

 as ' brands,' ' tufts,' and ' chalky patches.' Their action is to some extent under 

 the control of their possessor, the perfume being economised when not needed in 

 courtship. The scent adheres to the scales when removed from the wing, is 

 moderately volatile, and can be extracted with alcohol. 



The mode of distribution of the aposematic odours is not so easily determined. 

 They are, as a rule, strongly perceptible even in the uninjured specimen, but are 

 in some instances increased in intensity when the thorax is crushed, and they have 

 at times been found to be attached to the juices which in many species exude 

 from the body under pressure. 



The fact that, speaking generally, the agreeable fragrance belongs exclusively 

 to the males, while the repulsive odours are common to the two sexes, sometimes 

 indeed being stronger in the female, seems greatly to favour the interpretation of 

 their function above offered. And if this be the true explanation, it is very 

 remarkable that so much correspondence should exist between human aesthetic 

 preferences and those of some at least of the lower animals. 



Specimens of butterflies were exhibited showing (a) forms possessing an 

 epigamic scent, (b) forms aposematic ally scented, and (c) forms in which both 

 kinds of scent exist independently. • 



