THE SENSES AND THEIR ORGANS. 301 



words, when I blew upon her. the action of llio wind excited her, and 

 oiiused licr to i-ear upon lier hind legs as though some enemj' were ap- 

 proaching or some victim corning within reacli. 



This will . illustrate some of the difficulties in the way toward a just 

 verdict. Of course, all sound is produced by vibrations of the air ; but it 

 seems possible that the movements produced by tuning forks and other 

 instruments, sounded, as they must be, in so close proximity to the spider, 

 may and probably do mechanically agitate the hairs upon the body, and 

 thus effect the sense of touch alone, producing an excitement which I have 

 often observed and sometimes attributed to hearing. The difficulty has 

 been to separate between these two sensations and decide whether my ex- 

 periments had not simi)ly excited the spider by touch. My conclusion, as 



the result of independent observations, is that if spiders have 

 Organs of r i • ,i , .,..,',, 



Hearing. ^^^ ^^^^^ hearing proper, that sense is distributed, like the 



sense of smell, over the entire body; and, further, that it can 

 scarcely be distinguished from the sense of touch as it is known to us. 

 No doubt, however, the aranoad has some of the advantages within its 

 limited sphere that auditory organs proper give to higher animals. 



On this point the Peckhams also made a number of experiments, with 

 some interesting results, as follows : Certain spiders indicate that they hear 

 a vibrating tuning fork, by characteristic movements of the legs ; others by 

 signs of alarm, dro))ping from the web and keeping out of sight for a 

 longer or shorter time. One spider, at least, Cyclosa caudata, when sub- 

 jected to frequent approximations of a tuning fork, seemed to become grad- 

 ually accustomed to the sensation, and, instead of dropping from her web 

 as at first, remained immovable and apparently undisturbed. One of the 

 most interesting points developed is that orbmaking spiders appear to be 

 most sensitive to the vibrations of the tuning fork. All these responded 

 promptly, being evidently alarmed by the sound. 



On the contrary, spiders that make no webs gave not the slightest heed 

 to the sound. Among those species that proved unresponsive were two 

 Effects of '^'"^®^'^*^v*''''^ (Herpyllus), several Lycosids, and the familiar Dol- 

 Sounds.° omedes tenebrosus. Professor Peckham suggests that this differ- 

 ence may be partially explained by difference in the feeding 

 habits of the two groups, an explanation which leaves much to be ex- 

 plained. May we venture to suppose that, in the case of the Orbweavers, 

 the particular effect produced by the vibrations of the tuning fork upon 

 the spider hanging on her web, or upon the delicate filaments of the web 

 itself, is very nuicli the .same as that produced by the rapidly vibrating 

 wings of an insect when humming around the snare or when struggling 

 within it? Certainly Orbweavers are dependent upon some such agitation, 

 especially of the web, for the intelligence that their snares have succeeded 

 in trapping a victim. On the other hand, we know that Lycosids, for ex- 

 ample, which stalk their prey in the open field, instead of ensnaring them 



