go The Animal Mind 



non-irritating oils gave negative reactions (6i8) ; but an 

 oil that belongs, for us, to the latter class might belong 

 to the former in the case of a spider. If the sensibility 

 were sharply locahzed, that fact would point in the direc- 

 tion of a specific olfactory sensation; but while some 

 authorities think the spider's feelers or palpi are smell 

 organs (47), others believe that sensibility to chemical 

 stimulation is distributed over the body (452, 618). Nagel 

 finds no specific organ of smell and little smell sensibility 

 in spiders (522). 



A member of the Arachnida which presents but slight 

 superficial resemblance to the spiders is Limulus, the 

 horseshoe crab. Limulus shows taste reactions, but no 

 response to smell stimuli. If the mandibles at the base 

 of the legs be rubbed with inedible objects, there is no 

 reaction. Similar negative results are obtained by hold- 

 ing strong-smelling food close to the mouth or jaws. But 

 if an edible substance be rubbed on the mandibles, strong 

 chewing movements take place. Ammonia or acid vapor 

 will produce these same chewing reflexes, but the claws 

 make snapping movements "as though to pick away 

 some disagreeable object." If a wad of blotting paper 

 wet with ammonia or acid be laid on the mandibles, the 

 chewing movements are reversed and the object is some- 

 times picked up by the claws and removed. Patten found 

 organs which he believed to be gustatory on both the 

 mandibles and the claws (557). Pearl observed no gusta- 

 tory reactions in the free-swimming embryo of Limulus 

 (562). 



§ 23. The Chemical Sense in Insects 



Throughout all the branches of the animal kingdom thus 

 far mentioned, the chemical sense has functioned chiefly as 



