20 THE ZOOLOGIST. 
fully executed illustration of the organ by which the sound is 
produced.* 
From the knowledge thus supplied touching the function of 
the instrument in the Spiders just mentioned, one is perfectly 
justified in concluding that organs constructed upon the same 
principle, and occupying the same or similar positions, will in 
all probability be found to perform the same office; and no 
further basis need be sought for the belief that the African 
Spiders, Harpactira and Phoneyusa, and their allies, can stridu- 
late as well as their Oriental relations. 
Two other little points connected with the organs may here 
be mentioned. These are the fringes of hair surmounting the 
“notes” or vibrating bristles on the leg in Phoneyusa, and the 
pad of hair above the two series of bristles on the mandible of 
Harpactira. From the position of these hair-tufts it may be 
inferred that they serve to keep the bristles below them free from 
dirt, which would of course seriously interfere with the per- 
formance of their function. 
What now is the use to the Spider of the sounds that these 
organs give forth? It has been suggested that, like the call of 
the Cicada and the chirrup of the Cricket, they have a sexual 
significance, and serve to inform one sex of the whereabouts of 
the other. This belief, however, has no foundation in fact; for, 
in the first place, there is not a particle of evidence that these 
Spiders possess an auditory sense; and, in the second place, 
these stridulatory organs are equally well developed in the males 
and females, and are not, like the sexual stridulating organs 
known in other groups, confined to the male, or at all events 
better developed in that sex than in the female. Moreover, 
they appear in the young at an early age, and become functionally 
perfected long before the attainment of sexual maturity. So 
the supposition that they act as a sexual signal may be regarded 
as unsupported by evidence. 
As a matter of fact, the true key to their function is supplied 
by the behaviour of the living Spiders. From the accounts 
above quoted from Mr. Peal and Mr. Cambridge, it is evident that 
the Spiders emit the sound when on their defence and acting 
* Rep. Horn Exped. pt. ii. Zoology, pp. 412-414, pl. xxviii. 
