POWER OF HEAKING IN INSECTS. 75 



It would be, on the other hand, most unsafe to 

 conclude that spiders are incapable of hearing. Dahl * 

 has given reasons for believing that some of their hairs 

 serve as auditory organs. Westring has discovered, 

 in certain species of Theridium (T. serratipes, oculatum, 

 castaneicm, etc.), a stridulating organ, consisting of a 

 sort of raised bow attached to the upper part of the 

 abdomen, which rubs against the under and hinder 

 part of the cephalothorax, producing a whirring sound. 

 Lebert t naturally observes that this appears to indicate 

 a power of hearing on their part. 



As regards insects, it would be easy to multiply such 

 evidence almost indefinitely ; I have given more illus- 

 trations than I should probably have otherwise thought 

 necessary, because so excellent an observer as Forel, 

 whose opinion I should value on such a point as much as 

 that of any authority, expresses doubt whether insects 

 really hear at all. '' Ce qu'on semble," he says, in his 

 last memoir on the subject, " considerer comme preuve 

 de I'ouie me parait comme a Duges reposer a peu d'excep- 

 tions pres sur des ebranlements mecaniques de I'air ou 

 du sol qui sent simplement perfus comme tels par les 

 organes tactiles des insectes. Cela correspond a peu 

 pres a la derniere opinion de Graber sur " I'ouie " de 

 la Periplaneta. Mais on n'a pas le droit de nommer 

 ouie de pareilles sensations." J 



Graber, however, has endeavoured to meet this 

 objection by an ingenious experiment.§ He placed 

 some water-boatmen (Corixa) in a deep jar full of 



* " Das Gelior-und Geriichsorgane der Spinnen," Arch, filr Mie. 

 Anat, 1885. 



t " Die Spinnen der Schweiz." 



X A. Forel, " Sensations des Insectes," Becueil Zool. Suisse, t. iv. 1887, 



§ Arch, fur Mic. Anat, 1882. 



