312 



AMERICAN SPIDERS AND THEIR SPINNINGWORK. 



above facts he concluded, first, that the function of the three types of hair 

 above described cannot be recognized as identical ; and, second, that no one 



of these types can be regarded as an auditory 

 organ. 



But, if their function is not identical, their 

 fundamental likeness in anatomical structure 

 gives one a right to suppose that they do have 

 a function more or less analogous. Wherein 

 does that function consist ? Mr. Wagner con- 

 siders that the function of the Tactile hairs 

 ought to be more perfect than that of the 

 other types, because 

 of their more per- 

 fect structure, and 

 that, therefore, they 

 should be capable 

 of receiving more 

 delicate excitations 

 than the ordinary 

 Tactile hairs. One 

 use, he thinks, may 

 have been indicated 

 by Dahl, who re- 

 marks that the 

 slightest breath of 

 air is able to move 

 the auditory hairs, a 

 fact which may be 



readily observed ; at least, that spiders are always 

 extremely sensitive to the slightest puff of wind 

 made by the human mouth. There may, therefore, 

 be assigned to the auditory hairs the function of 

 transmitting the mechanical movements of the air. 

 Wagner again raises the conjecture that the 

 Beaded and Clubshaped hairs may be used to in- 

 dicate the state of the weather ; a conjecture which 

 he bases upon what he supposes to be an ac- 

 cepted fact, namely, that spiders are so sensitive 

 to weather changes as to be able to anticipate 

 them, and, indeed, to prognosticate them by their 

 behavior. That this is a widespread belief I else- 

 where indicate (in the chapter on General Habits) ; 

 but that it is without foundation, I think, I also show ; so that Mr. Wagner's 

 suggestion must fall to the ground before the presence of facts of habit. 



FIG. 296. Section of a fine Tactile hair, 

 p, the stalk of a hair ; r, the superior 

 thickening of the root in the cavity of 

 the large external pouch ; bo.e., cavity 

 of the large external pouch ; r 2 , basal 

 thickening of the root at the point of 

 its junction with the basal fold ; z, ele- 

 vation upon the superior part of the 

 basal thickening of the fold by which 

 the free borders are bent against the 

 stalk of the hair and form a little ex- 

 ternal pouch ; p.t.r., section of the 

 walls of the internal pouch, by which 

 the inferior part of the basal thicken- 

 ing of the fold (t.r.s.) is inserted be- 

 neath ; b, wall of the large external 

 pouch, corresponding to the annular 

 elevation of the first layer of chitine 

 in the Tactile hair. The other parts 

 corresponding to those of the Tactile 

 hair are marked by the same letters. 



FIG. 297. Section of the root of a 

 Clubshaped hair, m, the club- 

 shaped blade of the hair ; st, lon- 

 gitudinal striations of the blade ; 

 z, elevation upon the superior 

 part of the basal thickening of 

 the fold by which the free borders 

 are bent against the stalk of the 

 hair and form a little external 

 pouch ; r, root of the hair, with 

 its thickening; p.t.r., section of 

 walls of the internal pouch by 

 which the inferior part of the 

 basal thickening of the fold (t.r.s.) 

 is inserted beneath ; b, walls of 

 the large external pouch, corre- 

 sponding to the annular eleva- 

 tion of the first layer of chitine 

 in the Tactile hair. The other 

 parts corresponding to those of 

 the Tactile hair are marked by 

 the same letters. 



