226 PRINCIPLES AND CONCLUSIONS. 



meter and followed it as the pin covered with it was withdrawn. The second 

 wasp behaved in identical fashion, though it was unable to sip the honey, 

 while the first was absolutely unable to perceive the honey until the latter 

 was put in contact with its mouth or to follow as it was moved away. 

 To determine how acute the sense of smell is in bees, Forel placed some 

 hungry honey-bees in a glass box with a drop of honey covered with a disk 

 of wire screen with large meshes, through which the honey could be read- 

 ily reached. In spite of this they walked back and forth over the screen, 

 passing a hundred times within 2 or 3 mm. of the honey, without stopping 

 or suspecting the presence of the food they sought. As soon as the screen 

 was removed, they found the honey by chance and sipped it with avidity. 

 In agreement with Lubbock, it was concluded that honey-bees guide 

 themselves almost exclusively by sight, their antenna? being very short, 

 without clubs, and having olfactory terminations only on the internal 

 dorsal face. 

 The following conclusions were deduced with reference to smell : 



1. With many insects that guide themselves primarily by vision, as with dragon- 



flies and cicadas, the antennae are rudimentary and the sense of smell likewise. 

 At night such insects are immobile and by day all their acts are guided by sight 

 (the cicadas also perhaps by hearing). 



2. The sense of smell, notwithstanding the objections and the experiments of Graber, 



resides in the antennae, especially in the swollen or perfoliate part in which 

 the antennal nerve ramifies. 



3. With certain insects, especially the majority of the Diptera, the antennae are 



stiff and probably serve solely or almost so as an organ of smell. 



4. But with other insects they are mobile and serve at the same time to smell at a 



distance and to feel near at hand. This is true of Hymenoptera in the highest 

 degree. 



ForePs criticisms of Graber's results. — Emphasis was placed by 

 Forel upon the fact that we regard as odorous substances those that are 

 odorous for us, in spite of the fact that the study of animals shows enor- 

 mous differences between them in this respect, a substance extremely odor- 

 ous for one species being little or not at all for another. This general 

 fact was recognized by Graber, but his simple and uniform method of 

 experimentation failed to take account of it. Graber placed different 

 insects in the middle of a box divided into two compartments open below. 

 He put an odorous substance in the top of one of them and observed at 

 the end of a certain time the number of insects in each part. He employed 

 especially substances with strong and often corrosive emanations, and in 

 many cases found that insects deprived of their antennae behaved like 

 normal ones. But this was not always the case, Asphodius, for example, 

 ceasing to gather under cow-dung when the antennae were removed. 

 This was because Graber had made the proper choice, that of an substance 

 sought by this insect in nature. Moreover, he finally stated that a certain 

 degree of smell resided in the antennae. 



In the case of Lucilia caesar, Graber found that 169 normal flies col- 

 lected under putrid meat, while 92 were found on the other side, but with 

 the antennae cut off the respective figures were 101 and 39, which he 

 thought proved irrefutably that they had smelled the meat without the aid 



