On Stridulating- Organs in the Genus Scytodes. 371 
LI.—Newly-discovered Stridulating- Organs in the Genus 
Scytodes. By F. O. PickKARD-CAMBRIDGE. 
THE presence of organs, in various parts of the body of certain 
spiders, whose function seems to be primarily, at all events, 
the production of sound, has long been a matter of common 
knowledge to most arachnologists. 
These organs, usually consisting of a hard chitinous plate, 
whose surface is set more or less closely with transverse ridges 
or rough corrugations, on the one hand, in opposition to one 
Or more cusps, spines, or tubercles developed on some other 
adjacent portion of the structure, will always prove of great 
interest to the, scientific student as well as to the general 
nature-loving public ; the more so, perhaps, because their exact 
significance in the natural economy of their owners, and their 
ultimate value as factors in a natural classification of members 
of the order, have not yet been ascertained with any show of 
certainty. ' 
These “ organs of stridulation’’ are found developed on 
two widely different portions of the body—the abdomen on 
the one hand, and the mandibles on the other. Nevertheless 
in both cases they appear to be modifications of essentially 
the same plan; for whether they appear on the mandibles 
working in correlation with the adjacent femoral joint of the 
palpus or on the abdomen with the more or less produced 
basal margin of the cephalothorax, these organs consist of a 
series of grooves or ridges in cooperation with spines or 
tubercles, which, when in motion, pass over the former just 
as one might draw a stick rapidly over a series of wooden 
palings, with a somewhat similar effect, though on a very 
much smaller scale. 
Of the organs which are found on the mandibles and palpi 
none are more remarkable than those discovered by the late 
Prof. Wood-Mason, and recently described and figured by 
Mr. R. I. Pocock, of the Natural-History Museum, South 
Kensington, in several species of various genera of the Thera- 
phoside. In these the hairs become modified and highly 
specialized, forming very beautiful organs of sound. ‘They 
consist of a series of longer and shorter hard, shining, chitinous 
keys, fastened at one end, free at the other, and raised above 
the surface of the exoskeleton of the mandibles or palpus, as 
the case may be; for these keys are developed sometimes on 
the coxal joint of the palpus, sometimes on the outside of the 
mandibles, and in the ‘'heraphosid in both sexes alike. 
In Musagetes, for instance, the spines which play across the 
26* 
