1911.] NATURAL SCIENCES OF PHILADELPHIA. 41^ 



able to produce a ; stridulating sound. Montgomery (1909) stated 

 also that the genus Geotrecha, a drassid, exhibits a good case of stridu- 

 lation. In the theridiids and Geotrecha as yet the stridulation has 

 never been heard by the human ear. It cannot be a sexual call for 

 the sexes in Geotrecha show no responses whatever to the stridulation 

 of each other and do not even stridulate during the mating. Even 

 if the sound in the theraphosids and others is audible to the human ear,, 

 this need not imply that these araneads have auditory organs for it 

 is much more probable that such sounds serve only as a warning to 

 animals other than spiders. Therefore, when all the evidence con- 

 cerning the sense of hearing is summarized, I am convinced that spiders 

 have no such sense according to our present definition of that per- 

 ception. 



B. The Tactile Hairs.. 



Morphologically there are probably five or six different, kinds- of 

 hairs on the various parts of the bodies in different species of araneads. . 

 Physiologically, as far as we know, they may be divided into the spin- 

 ning hairs located on the spinnerets and the tactile hairs which include 

 all others found elsewhere. The latter group includes the large movable 

 spines, the so-called auditory hairs and the various types of tactile- 

 hairs. 



While searching for the sense cells of the Lyriform organs, 1 was 

 successful also in finding the innervation of two kinds of tactile hairs 

 and the muscles which move one of these. The ones without muscles - 

 I shall call fixed tactile hairs and those with muscles movable tactile 

 hairs. In diameter the movable hairs are the second largest of all. 

 kinds of hairs and in length they are either as long but usually longer 

 than any other type of hair; in Theridium tepidariorum they are 

 abundantly distributed on the four distal joints of each leg, but rather 

 sparingly on the other three joints of the legs and elsewhere, while on 

 the femur most of them are located at the distal end arranged in two- 

 circular rows on the two lines of articulation. While these hairs are 

 long, slender, more or less bent and can be moved only slightly, the 

 movable spines are generally short, thick, straight and can be moved 

 considerably. The former are certainly only a modification of the 

 latter. 



Fig. 7, from the trochanter of Pholcus, exhibits the complete inner- 

 vation of the fixed tactile hairs. The socket (sk.) here, as in other 

 cases where no muscles were observed, is like those of the movable 

 hairs. The nerve (N.) is considerably torn, but still the parts are very, 



