i8 95 . MUSICAL BOXES IN SPIDERS. 47 



of the mandible, and the scraper, which consists of several short 

 spines, is set upon the inner surface of the basal segment of the 

 palp (Fig. 4). The organ is thus structurally the exact opposite 

 of Wood-Mason's, and the differences between them point to diver- 

 gent evolution of the two groups of spiders. The strings in the kind 

 we are now describing are few in number, generally five or less, and 

 each consists of a long, tough, blade-like, feathery hair, which is 

 nothing but an enlarged and slightly modified representative of the 

 hairs composing the carpet which, in these spiders, clothes the middle 

 of the outer surface of the mandible. Fig. 3 shows the outer 

 surface of the mandible of one of the spiders of this group, named 

 Phormingochilus, from Borneo, with the carpeting of short hairs and 

 the strings below it ; and Fig. 5 is a side view of one of the strings. 



It may be asked, however, what direct evidence there is that 

 the function of this organ is to make sound, and we are bound to 

 admit that there is none, except such as the argument from analogy 

 is capable of supplying. But it must be confessed that the assump- 

 tion is justified by the well-ascertained fact that in the allied group 

 possessing Wood-Mason's organ, which is made on the same principle, 

 at least one species has been heard to stridulate. In fact, it was 

 hearing the sound made by the animal that induced Wood-Mason to 

 look for its cause and led to the discovery of the organ above described. 

 And since the spider when stridulating was . observed to rub its 

 mandibles and palpi together, the fact that the sound was produced 

 by the friction is practically beyond dispute. 



But although we may thus claim clearly to understand the 

 mechanism by which the sound is made, we are by no means so sure 

 of its object. Since the organ is equally well developed in both 

 males and females, there is no reason for supposing, with Wood- 

 Mason, that the sound is used as a sexual call, as in the case of the 

 small spiders (Lephthyphantes and Thevidium) mentioned above, where 

 the organ is found perfected only in the male. Moreover, although the 

 last-named spiders belong to a group of which the members respond 

 readily to such sounds as those produced by a tuning-fork, all experi- 

 ments that have been made upon cursorial species, like Thomisoides and 

 the large bird-eaters, have failed to reveal the existence of any sense 

 of hearing. Consequently, in spite of Dr. McCook's argument, which 

 is clearly fallacious, that " of course the existence of stridulating 

 organs, if they be sound-producing organs, naturally infers the 

 presence of auditory organs," it may be safely stated that there are 

 no grounds for supposing that these spiders can hear the sounds that 

 they themselves produce. 



What is actually known about the question is briefly this. A 

 Mr. Peal,, who was the first to notice the sound, had his attention 

 drawn to the spider by hearing it stridulate loudly, when threatened 

 with death from the luckily ill-directed blows of a gardener's hoe. 

 Moreover, the rescued animal subsequently repeated the performance 



