c^6 William Morton Barrows 



worm appears to move directly away from the light without notice- 

 able trial movements. 



It seems to me probable from experiments described by Pearl 

 ('03, pp. 623-670) that planarians may follow some such method 

 in finding food. However, as the animal is not highly special- 

 ized, the distance through which it can orient accurately is small 

 and the result is not striking. 



IV SUMMARY 



1 Drosophila ampelophila is a small fly peculiar for its fond- 

 ness for fermenting fruit. 



2 These flies are positively chemotropic to amyl and especially 

 ethyl alcohol, acetic and lactic acid and acetic ether. 



3 Acetic ether, isobutyl acetate and methyl acetate, when 

 added in small amounts to 10 per cent ethyl alcohol, greatly increase 

 its attractiveness. A similar increase is noted where acetic or 

 butyric acids are added to the alcohol. All these organic sub- 

 stances are found in fermenting fruits. 



4 The optimum strengths of ethyl alcohol and acetic acid as 

 determined by the number of positive reactions given to diff^erent 

 strengths is 20 and 5 per cent, respectively, while a mixture con- 

 taining 2^ per cent alcohol and f per cent acetic acid gives a 

 slightly higher number of positive reactions than is given by either 

 5 per cent acetic acid or 20 per cent ethyl alcohol. Alcohol and 

 acetic acid are commonly found in cider vinegar, fermented cider, 

 and California sherry in per cents that are close to those which 

 call forth the largest number of reactions in Drosophila. 



5. Drosophila does not find its food by sight, but by smell, and 

 when this sense is lost it reaches its food only by accident. The 

 olfactory sense organs — at least those which are concerned with 

 finding food — are located in the third or terminal segment of the 

 antenna. 



6 When one antenna is lost and the other antenna is stimu- 

 lated by food odor, circus movements are carried out in such a way 

 as to prove that the fly orients normally by an unequal stimulation 

 of the antennae. 



