XXVlll 



formed by a sharp-edged lamellar projection on the meropodite of each of 

 the chelipeds, and the rasp was the crenulated infraorbital margin ; in 

 these the apparatus could only be developed in the males, the females 

 having short and small and quite inconspicuous chelipeds, which hardly 

 reached so far as to the margins of the orbits. In others (II.) they were 

 seated wholly on the ajjpeudages ; in the males of the species of Ocyjjode 

 the I'asp was on one and the scraper on another part of the same appendage • 

 in those of PlatyonycJnis hipustulosus the rasps were on one and the scrapers 

 on another pair of appendages ; the walking-legs of the second pair were 

 here very long and robust, and their third joint (meropodite) had its upper 

 margin produced upwards at apex into a sharp crest (the scraper); both 

 Dana and Milne-Edwards had noticed the remarkable length and structure 

 of this pair of legs, but the former alone had mentioned, in his description 

 of the species, the regular transverse plicatioii of the under surface of the 

 propodite of the chelipeds, which constituted without doubt the rasp. The 

 above did not pretend to be a complete account of stridulating apparatus 

 in Crustacea ; but separated as he at present was from notes, drawings, and 

 specimens he could not go into greater detail. The cases of Macrophthalmus 

 and of Platyonych'us had not, he believed, been previously recorded. In the 

 forms alluded to by Mr. Kent no special sound-producing apparatus seemed 

 to be developed. Everybody who had searched for animals on coral-reefs 

 or had dredged in tropical seas was familiar with the "clicking" sounds 

 emitted by the Aljthei and their allies. The sounds which here always 

 accompanied so sudden an opening of their claws to their fullest extent that 

 dislocation seemed imminent each time, might be caused either by the im- 

 pact of tlie dactylopodite upon the joint to which it is articulated or by the 

 forcible withdrawal of the huge stopper-like tooth of the dactylopodite from 

 its pit in the immovable arm of the claw ; in which latter case the noises 

 might be susceptible, mutatis mutandis, of the same physical explanation 

 as that produced by the withdrawal of a tightly-packed piston from a cylinder 

 closed at one end. These were the explanations that occurred to him while 

 watching a small species that lived in force amidst the branches of the 

 zoophytes called Spongodes, the masses of which crackled all over when 

 brought to the surface. The sounds in this case resembled very closely those 

 made when sparks were taken by the knuckles from the prime-conductor 

 of a small electrical machine. The sounds emitted by the Sphseromid 

 might possibly be produced by the impact of the terga of the posterior 

 somites upon one another at the end of each movement of extension. 



Mr. Wood-Mason then announced the discovery of stridulating organs in 

 PhasmidcB, in a species of Pterinoxylus, and in illustration of his remarks 

 exhibited an impression of Westwood's plate of Serville's species, P. diffor- 

 mipes. Here, as in Crustacea and some other Arthropods, an apparatus 

 working perfectly independently of its fellow was developed on each side of 



