CHEMICAL REACTIONS OF FRUIT-FLIES. 301 



My original view that these smells were direct sexual guides emitted by the 

 females is quite unproved. In my former paper I described two experiments in 

 smelling the females ; in the first, an extremely faint aromatic smell could just be 

 perceived, and in the second (with a larger number of females) a more distinct 

 " citronelloid " smell, which was independently confirmed. Unfortunately, I dis- 

 covered subsequently that for reasons against which it would be, in a civilised 

 country, unnecessary to guard, this second experiment must be completely rejected. 

 In the summer of this year I took several lots of living females, crushed their bodies 

 between clean slips of glass, and exposed them in a place where males were present 

 in some numbers, but they had no attraction whatever for the males. These females 

 were all individuals that had emerged within the previous thirty-six hours, and 

 the experiment to be quite conclusive should be repeated with an older batch. 



If the smell is not a direct sexual guide, it might be 



(a) a food-smell ; involving the assumption that the feeding habits of the males 



are quite different from those of the females; 

 (6) a " rendezvous " smell, guiding males to the eugenol-derivative-producing 

 plants on which the females were accustomed to rest ; involving the 

 assumption that the females decided on their resting-places for other reasons. 



There are three plants on which males, but never females, have been seen to 

 congregate in large numbers. These are the flowers of the Papaya (visited by 

 diversus and ferrugineus), the female inflorescence of an Australian Cycad, and the 

 spadix of the Aroid Colocasia antiquormn (both visited by zonatus and some 

 ferruginens). In none of these three plants have any of the flies been known to 

 breed. All have a very uncommon smell, resembling that of eugenol derivatives. 

 The males which congregate upon them seem to suck the surface of the plants, and 

 this is consonant with a food-smell hypothesis, but they do not seem to exhibit any 

 very special avidity. I have not been able to get any information as to whether or 

 no eugenol-derivatives occur in the normal food-plants of the larvae. 



Mr. C. S. Misra has collected diversus males which were swarming about mango- 

 flowers in Coimbatore ; it is noteworthy that diversus never, so far as I know, 

 breeds in mangoes. Mr. Kunnikannan has, however, bred what is probably 

 ferrugvneus from a species of Eugenia at Bangalore, and as the genus Eugenia 

 constitutes the main source of eugenol, some connection seems here to be indicated. 

 On the other hand, although zonatus, ferrugineus, cucurbitae, caudatus, and (I believe) 

 diversus, have all been observed, both males and females, resting under the leaves 

 of the Jammi-tree {Eugenia jambolana) at Pusa, none have been found breeding in 

 the fruits in spite of careful search. 



The fact that the reaction is rigidly confined to the male sex is difficult to explain 

 by supposijig it to be due to food-smells or other attractive smells emitted by 

 plants or flowers, unless indeed we suppose that the males thus find out the eugenol- 

 derivative-produciug plants wliere the females are likely to be. It is noteworthy 

 that the males are not ordinarily seen at other flowers. In order to explain the 

 absence of females on the Papaya, Cycad, and Colocasia, we should then have to 

 suppose that since females are never seen at these plants they must either (1) have 

 food-tastes quite distinct from those of the males, or (2) must have an entirely 

 different method of finding their resting-places. 

 (C205) G 



