330 EDWARD F. ADOLPH 
Two distinct reactions were required in these trials: 1) ap- 
proach to a distant attraction, and, 2) extrusion of eggs. 
1. Controls. .The simplest environments that could be pre- 
sented for the competitive attraction of the flies were glass 
vials without moisture, odor, or other contents. No flies entered 
such traps. But when absorbent cotton saturated with water 
was placed in the vials a few eggs were laid, averaging 0.005 per 
day per fly, as shown in table 1. 
2. Taste. Materials were chosen which, while having no 
odor, had taste which might be sensed through contact, using 
the human senses as an arbitrary means of judging the properties 
of substances. ‘These were all used in water solutions, usually of 
1 to 10 per cent. No responses were obtained which surpassed 
those toward water alone, the only stimulating solutions of those 
tested being oxalic acid and citric acid (table 1). 
3. Odor. The substances possessing odor that were used 
were chiefly the simple organic acids, alcohols, and esters. Solu- 
tions of these were absorbed in cotton within the traps, and con- 
tact with the solutions prevented by partitions of perforated 
blotting-paper. No moist surfaces were accessible to the flies. 
The flies responded in small measure to acetic acid, ethyl acetate 
and alcohol, amyl alcohol, and amyl valerianate (table 1). 
4. Taste and odor. A large variety of odorous substances 
were used in a manner similar to that of the last experiment, ex- 
cept that the female flies were allowed to come in contact with 
the solutions after they had approached the traps. The majority 
of the organic compounds tried called forth small amounts of 
egg-laying, as shown in table 1. 
Summary. From these experiments it is evident that moisture 
alone is conducive to egg-laying in very small amounts, that 
taste plays no definite réle in initiating the response, while odor 
is a slight stimulus, especially when the odorous solution may be 
approached and touched. Moreover, the flies are readily at- 
tracted toward odorous substances, and in agreement with Bar- 
rows (’07) the most attractive of these proved to be acetic acid 
and ethyl alcohol. 
