428 N. E. MCINDOO. 



doubt as to whether the insect moved for any reason other than 

 the olfactory stimulus, such movements were never recorded. 

 The reaction time was counted in seconds. With an ordinary 

 watch the minimum time which can be definitely recorded is two 

 seconds, although many of the individuals responded to some of 

 the odors much more promptly. Owing to this source of error, 

 the average recorded time is probably double what it should be 

 in the cases where all the responses for the same insect were 

 prompt. An intermission of lo minutes elapsed between any 

 two tests in the same experimental case. Each individual was 

 tested only once with the same odor. 



In recording the responses the term '.'vibrated" is used to 

 describe the rapid movement of the antennae or legs up and down 

 or from side to side. When this movement is slow, these ap- 

 pendages are described simply as having "moved." When the 

 antennae, legs or mouth parts are moved so that they are quickly 

 bent at their articulations, they may be described as being 

 "worked." When at rest a beetle usually lies fiat on its thorax 

 and abdomen, so the word "arose" means that the insect gets 

 up and stands on its feet. In the averages of reaction times the 

 probable error is presumably high. It has not been calculated 

 since slight differences in reaction times are not considered as 

 significant in the discussion of results, All anthropomorphic 

 terms are put in quotation marks. 



CARABID^. 



The Olfactory Sense of Harpalus pennsylvanica . 

 Many ground beetles {Harpalus pennsylvanica) were caught 

 under fiat stones in a corn field near the laboratory. As soon as 

 brought to the laboratory, 25 of them were placed singly into 

 the experimental cases. As they were being placed into the 

 cases, some of them discharged a substance, presumably from the 

 anal glands, which gave off an odor similar to that from formic 

 acid. Confined in these cases, they sought the dark corners of 

 the cases and did not wander about much inside the cases unless 

 irritated. When half hidden in the dark corners, they rarely 

 responded to odors, so it was necessary to keep them out of the 

 corners while they were being tseted. The longer they remained 



