310 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



J 



Several illustrations of the types of hairs known as auditory are here 

 reproduced from the latter writer. Their character is well enough ex- 

 plained in the legends of the cuts, but a brief description may be added. 

 The two parts of the hairs are distinguished as the root and the stalk or 

 shaft. By the root is understood that portion which enters the cuticle, 

 and is inserted into an appropriate pit ; by the stalk the free part of the 

 hair which extends above the cuticle. The hairs of spiders, both by their 

 structure and their root, appear to be divided into two principal types, 

 perfectly distinct. One sort is distinguished by a root which is much 



larger than the portion of the stalk im- 

 mediately above it. In other words, the 

 stalk narrows at its foot to swell out 

 again into a much enlarged root, thick- 

 ened into the form of a button and in- 

 serted into a sac like cavity of the skin. 

 (See Fig. 294.) This is what AVagner 

 denominates a Tactile hair, proper. The 

 roots of the other sorts of hair are ordi- 

 narily much smaller, as compared with 

 their stalks, than the type above named. 

 (See Figs. 295 and 297, r, r, compared 

 with Fig. 294, r, r.) The hair pits or 

 follicles enclosing the roots are also more 

 simply constructed. 



Tactile hairs (}>oils tactiles) are en- 

 dowed with extreme sensilnlity, as is 

 manifest from the fact that the lightest 

 filament of silk can at once be detected 

 by them and communicated to the ani- 

 mal. The other types are simpler in 

 their structure and, perhaps, their func- 

 tion. Dahl does not make any distinc- 

 tion between the hairs of the different 

 types, and names them all auditory ; but 

 "Wagner distinguishes the hairs into three 

 principal types, the Tactile hair, including one of finer structure (poil tactil 

 fin), the Beaded hair (poil a chapelet), and the Clubshaped hair (poil 

 cucurbitiforme). 



The principles that led Dahl to attribute to his auditory hairs this 

 function restg alone upon the fact that the waves of sound set them into 

 motion, which movement is borne along the extremity of the nerves and 

 provokes the sensation of sound. 



He appears to attribute the same function to all the types of hairs 

 distinguished by Wagner. In this opinion the latter author cannot agree, 



W 



jnt. 



Fig. 294. Transverse section of a Tactile hair in 

 the foot of a spider. (After Wagner.) oh, 1, 

 2, 3, 4. -5, laj'ers of chitine ; nit, the matrix of 

 the hair ; t. tube formed b.v the inferior layer 

 of the cuticle Ich. 5|. and filled with plasm, 

 pis; pi, fold formed by the tube (t) at the 

 level of the first layer of the cuticle ; t.r.s., 

 inferior part of the basal thickening of the 

 fold ; t.r.a., its superior part ; r. central part 

 of the radix of the hair ; c, papilla ; o, orifice 

 of the root by which the plasm passes from 

 the cavity of the tube into the cavity of the 

 hair, x ; N, the nerve ; p, the stalk of the 

 hair ; b, the annular thickening of the supe- 

 rior layer of the cuticle surrounding the root 

 of the thread. 



