14 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



are slightly too high for those insects which did not respond readily ; 

 but the figures given under the heading " difference " are practically 

 the same as those when all the insects counted in section i were 

 eliminated. 



Usually during the afternoon similar tests were conducted four 

 times, using the same beetles, but no light was used. In this case, 

 without the use of light, the geonegative response was 5.27 ±0.177 

 more than the geopositive one, while with the use of light it was 

 only 2.40±o.i2o more (table i), 10.00 being equal to a 100 per cent 

 response. 



On later dates the preceding tests were again repeated, using two 

 other sets of overwintering beetles. The general average and prob- 

 able errors of the three series were therefore obtained by using the 

 12 means and the mean of them. Thus, for active, overwintering 

 beetles the geonegative response, when light was used, was 2.56 ± 

 0.140 more than the geopositive one; but when no light was used, it 

 was 5.46 ±0.1 19 more, indicating that when the beetles were forced 

 downward by the light this stimulus overcame about one-half of the 

 geotactic one. In two of these series of tests the light was used 

 during the forenoon, but in the third series during the afternoon. The 

 sequence in which these insects were tested, therefore, had little or 

 no effect on the results obtained. 



The preceding tests were repeated by using one set of old beetles 

 of the second brood. These insects were not so active as they were 

 when younger and did not respond so readily to light and gravity 

 as did the more active overwintering beetles. Their lower responses 

 were due mostly to the fact that the insects soon became tired of 

 being forced to respond. 



Two sets of larvae were likewise tested in the photo-geotactic box 

 and were found to be photopositive and geonegative (table i). Com- 

 pared to the adults they were sluggish and three times in four did 

 not respond as readily to light and gravity. Larvae of the third 

 instar reacted weakly to light and gravity, while the larvae of the 

 fourth instar responded strongly to light but weakly to gravity. 



The reader has doubtless noted that the writer has designed his 

 experiments and discussed his results from the point of view that 

 rate of movement is a measure of tropic response. After an animal 

 is oriented, some writers claim that the rate of its movement toward 

 or away from the source of excitation is not a measure of its tropic 

 response. If a tropic response includes nothing more than the mere 

 act of orienting, the preceding results then have little to do with the 

 subject of tropisms. The writer in various publications has dis- 



