84 The Animal Mind 



and other irritants (22). Evidences of irritation by the 

 neighborhood of asafoetida were observed also by Graber in 

 Pagurus (152). 



In some Crustacea the sense of smell is possibly concerned 

 in guiding the male to the female. Certain copepods which 

 daily migrate from near the surface of the water to greater 

 depths and back again have had this behavior explained as a 

 result of the reactions of the females to light, plus the tendency 

 of the males to follow the females. That the latter is an 

 affair of chemical stimulation is indicated by the fact that the 

 females were sought even when concealed hi tubes (304). 

 In the case of some other Crustacea, however, the sexes do not 

 seem to be aware of each other's neighborhood until they come 

 into actual contact (182, 184). 



24. The Chemical Sense in Arachnida 



The two most important divisions of the phylum Arthro- 

 poda, besides the Crustacea, are those of the Arachnida and 

 Insecta. Spiders, as is well known, have highly developed 

 ^ responses to mechanical stimulation ; the web-making species 

 in particular are sensitive to very slight web vibrations. The 

 food reactions of spiders have never, so far as the writer knows, 

 been tested, but various observers report sensitiveness to 

 chemical stimulations, such as those produced by odorous 

 oils, not in contact with the body. Spiders of the family 

 Attidae would react to glass rods dipped in such oils and 

 brought close behind them, but would not react to clean glass 

 rods when similarly placed (320). The reactions seem to be 

 of a negative character (351), and, of course, in all such cases 

 it remains uncertain whether the possible conscious accom- 

 paniment is a specifically olfactory unpleasantness or an un- 

 pleasant irritation of the body surface. Pritchett found that 

 irritating and non-irritating oils gave negative reactions (351) ; 



