CHEMICAL REACTIONS OF FRUIT-FLIES. 299 



alcohol) ; this treatment converts eugenol into the isomeric compound iso-eugenol. 

 The relation between the two compounds is shown by the formulae below, the 

 hexagons being benzene rings : — 



HO /\ HO y\ 



CH3O 





CH2 . CH : CH2 







CHiCH.CH. 



\y 



CH30 \y 



Eugenol. 



IS( 



)- eugenol. 



It will be seen that the difference lies in a rearrangement of the hydrogen atoms in 

 the side-chain. The effect of boiling with amyl alcoholic potash was vastly to 

 enhance the attraction of clove oil for diver sus, so much so that it competed 

 successfully with citronella. It appeared also to be somewhat attractive to 

 ferrugineus, but less so than to diversvs ; zonalus had not appeared at this season. 



The relative attraction of bay oil and citronella were next tested by exposing 

 a rag wet with citronella and a bowl of water into which a little bay oil had been 

 stirred. The rag and bowl were placed a few feet apart. The result was that iji 

 two hours 32 diversus and \i ferrugineus were caught on the citronella rag, while the 

 bay oil was visited exclusively hj ferrugineus and 27 of this species were caught at it ; 

 zonatifs did not appear (10.iii.13). Citronella contains methyl-eugenol and very 

 probably also eugenol and iso-eugenol ; bay oil contains methyl-eugenol and 

 eugenol. 



This result was the first definite indication of the possible existence of specific 

 attracting substances for diversus and ferrugineus respectively. As zonatus was 

 still absent or exceedingly scarce, it was not yet possible to observe its behaviour 

 towards the two oils. As I have said above, at the time when my former paper on 

 this subject was written I Tegarded ferrugineus and zonatus as being no more than 

 varieties of the same species. My immediate object now was, assuming the 

 " ferru^ineus-attT3i>ctoi " present in bay to be one single compound (methyl 

 eugenol ? ) and not a mixture, to obtain a pure sample of this compound. On my 

 view that the attraction was to be regarded as a specific character, it follows that 

 such a pure sample could be used as a touchstone on zonatus to determine its degree 

 of affinity to ferrugineus. The natural oil-mixtures are so complex and so often 

 adulterated that they are untrustworth}^, 



I procured from Messrs. Merck samples of eugenol, iso-eugenol, methyl eugenol, 

 and berfczo-eugenol. By the time I was able to test them (May) all three species, 

 diversus, ferrugineus and zonatus, were present, but typical ferrugineus were rare, 

 the form present in fair numbers being the intermediate one shown in fig. 2, PI xiii. 

 I exposed these four substances in the usual way in small basins placed a foot apart 

 on a table in my garden, each basin containing about a pint of water with a few 

 drops of the substance stirred up in it. The result was very interesting :• — 



Eugenol attracted nothing. 



Iso-eugenol attracted diversus very strongly ; a few ferrugineus. 



Methvl-eugenol attracted zonatus very strongly ; many ferrugineus. 



Beiizo-eugenol attracted nothing. 



