XXX THE VOYAGE OF H.M.S. CHALLENGER. 



described and figured by Professor T. J. Parker, 1 who says that Mr. Saville Kent remarked 

 in Nature 2 upon the shrill squeaking sound emitted by living specimens of Palinurus 

 vulgaris when handled, this sound being due, according to Mr. Kent, to the friction of 

 the abdominal somites ; and Mr. Parker suggested that the noise referred to may possibly 

 have been produced by the apparatus described. 



Dr. Mobius attributes the sound made to the action of innumerable close-set minute 

 hairs inclined with their points upwards, situated on the lower surface of the flap, which 

 plays over the lateral ridge of the antennular sternum ; but with regard to the statement 

 that it is the friction of the flap, and not of the pad, which produces the sound, Mr 

 Parker 3 says that he has "removed the flap entirely without any sensible diminution of 

 the noise. The mere observation of the parts while in action is enough to show the true 

 state of things : when looked at from the front it is very evident that the flap exerts hardly 

 any pressure upon the ridge, as, indeed, from the fact that it is a soft structure supported 

 only along one edge, it could scarcely be expected to ; while the pad, on the other hand, 

 is completely flattened out against the smooth surface, and in the most perfect contact 

 with it." Mr. Parker also remarks : — " In the matter of histological structure, the pad 

 does not differ from other chitinous membranes, being formed of fine superposed horizontal 

 laminee, marked by a vertical striation. It is, however, of unusual thickness ; and its 

 horizontal laminae have, for some distance down, a varying appearance, corresponding 

 with the ridges into which the surface is raised. The stridulation is almost equally 

 audible in water and air." I have produced it with specimens taken out of spirits, 

 but it soon wore off. Dr. Mobius and Mr. Lloyd heard it in the Hamburg Aquarium ; 

 and Mr. Parker observed the sound and the movement of the antennae producing 

 it in a specimen brought alive to the Biological Laboratory of the School of Mines. 



A similarly formed stridulating organ exists in the genus Panulirus, but in the 

 closely allied genus Palinosytus the inner articulating process is attached, and works as a 

 movable hinge, and there is consequently no stridulating organ ; nor is there any in the 

 genus Synaxes. 



This second joint of the peduncle is peculiar throughout the whole of the Macrura, 

 in having attached to it an articulating appendage, the scaphocerite, excepting in the 

 tribe Synaxidea, and in the genus Nephropsis among the Homaridse. In the family 

 Scyllaridae, the first joint is fused with the cephalon and the third is peculiarly produced 

 on the outer side to form an elongated plate ; the fifth, which represents the flagellum, 

 is produced in this family in the form of a large, broad, thin, disc-like plate. 



In the Astacidse, of which Homarus is the most perfect type, the scaphocerite exists 

 probably in its most normal condition, and has a rigid external margin produced to a 



1 Proc. Zool. Soc. Lpnd., pp. 298, 442, 187S. 



2 Nature, November 1877. 

 z Loc. cit., p. 443. 



