146 



PRINCIPLES AND CONCLUSIONS. 



While the heads with red and white squares seemed to be much more 

 attractive, this was shown not to be wholly true by the next test, in which 

 the application of white or green disks to the center of the heads resulted 

 in masking the latter entirely. In spite of this, a total of 29 visits was re- 

 corded, of which the black square with white disk received 7. However, 

 the red square with white disk still yielded the largest number, and a direct 

 comparison between black and white was lacking, as no white square 

 was employed in this series. Similar results were obtained with a disk 

 masking the tubular flowers alone, and with a central cylinder and a black 

 square. 



In order to avoid objections arising from the use of paper, the latter 

 was replaced by leaflets of Ampelopsis in the remaining experiments. 

 When the rays of 20 heads much sought by insects and well distributed 

 among normal heads were covered with leaflets, with only the yellow disk 

 in evidence, 36 visits were noted in an hour, 18 by Bombus, 11 by Vanessa, 

 and 7 by Megachile. To determine whether the yellow disk still furnished 

 the necessary attraction, this was effectively concealed in each of the 20 

 heads by a smaller leaflet. In spite of this an hour period yielded 58 visits, 

 of which 28 were made by Bombus, 6 by Vanessa, 5 by Pieris, and 1 by 

 Megachile. The following day the small leaflet was placed in contact with 

 the disk-flowers in 16 heads and these were disposed among a larger number 

 of normal heads. Of the 30 visits made, Bombus afforded 19, of which 13 

 were successful and 6 in vain, while the butterflies made 6 unsuccessful 

 to 3 successful ones. In the fourth series 37 heads were completely covered 

 with leaflets and the remaining ones were removed. In an hour's time 70 

 visits were recorded, distributed as follows. 



The author contended that the experiments of Bert, Lubbock, and 

 others gave misleading results, since it was impossible to give two dif- 

 ferent colors the same absolute intensity. This conclusion was derived 

 from the researches of Graber (1884), who found that leucophile, i. e., 

 light-seeking, invertebrates preferred the more refrangible rays, while the 

 leucophobe chose the less refrangible, red producing to them the effect 

 of obscurity. He also cited the observations of Forel (1887) and others to 

 the effect that the sense of smell is much better developed among insects 

 than in man, and that the perception of odors is very different. From these 

 facts he reached the conclusion that nothing in our present knowledge 

 proves that insects distinguish colors as the human eye does, and also that 

 they perceive odors that can not be recognized by the olfactory nerve 

 of man. His final conclusions were as follows: 



