300 F. M. HOWLETT. 



At this season diversus was not abundant, but the numbers of both diversiis and 

 zonatus which came to the iso-eugenol and methyl eugenol respectively, and the 

 promptness with which they appeared at the bowls, were very striking. As I walked 

 carrying the methyl-eugenol bowl, from my bungalow to the table on which the 

 bowls were exposed, a distance of about fifty yards, it was most pleasing to see three 

 zonatus settle on the bowl before I had reached the table. Similarly, six diversus 

 were noted at iso-eugenol when it had been in place five minutes. In two morning 

 exposures of about two hours each 275-300 zonatus were fomid drowned in the 

 methyl-eugenol bowl, and 48 diversus in iso-eugenol. The quantity of each substance 

 in a pint of water was about 2 cc, but 0*5 cc. was equally effective. 



The attraction of ferrugineus was apparently not quite so definite ; though the 

 majority of those seen went to the methyl-eugenol, iso-eugenol seemed (pardcularly 

 when stale) to have an attraction for them. On some occasions a certain number 

 of zonatus have also been seen at iso-eugenol, once or twice when methyl eugenol 

 was not present, often when the iso-eugenol bowl was to leeward of one containing 

 methyl-eugenol. Under these circumstances the flies, which seem invariably to 

 come up the wind, if there is any, will often explore and sometimes remain in bowls 

 which contain substances other than the one they presumably came for. 



At one period, after rather heavy rain has fallen, some very anomalous results were 

 obtained, but it appeared that these were due to rain-splashes from the different 

 bowls, which were then placed at a distance of not more than about eight inches 

 one from another. After cleaning the bowls and table with kerosene and spirit, the 

 flies difierentiated as usual. The delicacy of their perception will always introduce 

 error unless care is exercised in filling and handling the bowls, for the trace of a 

 thumb very slightly tainted with iso-eugenol has twice been seen to collect quite a 

 little crowd of diversus at a control bowl filled with water. The attraction of methyl 

 eugenol for zonatus and ferrugineus is very distinctly greater than that of the same 

 quantity of bay oil, which again is greater than that of citron ella. In the same way the 

 attraction of iso-eugenol for diversus is very much greater than that of citron ella. 



The sharp distinction between the strong attraction of iso-eugenol for diversus 

 and the relative failure of the isomeric eugenol (possessing a very similar kind of 

 smell) is of interest. My experiments as a whole indicate that diversus is, 

 practically speaking, not attracted at all by eugenol or methyl eugenol, though 

 certainly ifc cannot be said that either is distasteful ; zonatus, strongly attracted 

 by methyl eugenol, is practically unaffected by eugenol or iso-eugenol, though 

 it has perhaps a slight inclination to the former, and neither of them is distasteful ; 

 ferrugineus is not definitely attracted by eugenol, but may otherwise be said to 

 be intermediate between zonatus and diversus, being definitely attracted by both 

 methyl- and iso-eugenol. The definiteness of the reaction is indicated by figs. 



In fig. 2, PI. xvi., the two patches of moisture at the right and left-hand bottom 

 corners of the paper represent dabs of a substance purchased as " methylate of iso- 

 eugenol." This substance attracted all three species. I have not yet ascertained 

 its actual composition ; if it is the compound methylisoeugenol, the fact of its 

 attracting all three species is of considerable interest, but it is otherwise if it is merely 

 a mixture of methyl- and iso-eugenol. 



