Jan., 1895. 



MUSICAL BOXES IN SPIDERS. 



45 



Beneath the forepart of a spider's head there is, on each side, a 

 stout jaw, which ends in a long, moveable, claw-like fang. Immediately 

 behind this jaw, or mandible as it is called, there is a short limb, 

 formed almost exactly like one of the walking legs. This limb, known 

 as the palp, is never used for locomotion, and is directed straight 

 forwards in such a manner that the inner surfaces of its basal 

 segments are closely applied to the outer surface of the mandible. In 

 most cases these surfaces are smooth, so that they slide over each 

 other with but little friction, and practically no noise ; but, as has 

 been already described, in some species of Lephthyphantes the 

 opposed surfaces are finely ridged. Consequently, friction and 

 sound must ensue when the surfaces are rubbed together. But as a 

 matter of fact, owing to the small size of the spider and the fineness 

 of the ridges, the sound produced is, according to Mr. Campbell, too 

 slight for human ears, even when supplied with a microphone. 



In another spider, however, named Thomisoides, which is found 

 only in the southern hemisphere, and is about equal in size to our 

 largest British species, the stridulation is, accord- 

 ing to M. Simon, distinctly audible. The instru- 

 ment in this case resembles in structure and 

 position that of Lephthyphantes, except that the 

 scraper consists of a series of sharp tubercles on 

 the inner surface of the third segment of the palp 

 (Fig. 2). These tubercles, by being scraped up 

 and down over the ridged area on the outer 

 surface of the mandible (Fig. 1), give rise to a 

 sound which is said to resemble the buzzing of 

 a bee. Lastly, it must be added that, whereas in 

 Lephthyphantes it is the male that is supplied with 

 the more perfect instrument, in Thomisoides the 

 two sexes possess it equally well developed. 

 In the last group that has to be considered the organ is also 

 present in the males and females ; but it is more complicated, and 

 differs greatly in structure from those that have been just described, 

 since it consists exclusively of modified hairs. The organ was first 

 noticed by the late Professor Wood-Mason, who discovered it in a 

 huge Indian spider, to which he gave the name Mygale stvidulans. 

 Most of our readers are probably aware that the Mygalidae, or Avicu- 

 lariidae as they are more properly named, are the largest spiders 

 known, being in fact those that are often called the " bird-eating 

 spiders." Still the sounding organs are not found in, by any means, 

 all the members of this group. Indeed, since 1876, when Wood- 

 Mason's paper was first published, no author has until now taken the 

 pains to re-investigate the question, or to discover in which species the 

 organ is present and in which absent. But a recent examination of 

 the spiders of this family contained in the British Museum has shown 

 that all the large kinds that are found in the countries lying between 



Figg. i and 2. — 

 Mandible and palp 

 of Thomisoides. 



