Page:The Zoologist, 4th series, vol 2 (1898).djvu/46

20 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 stridulate 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 performance 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