OCR Text |
Show 292 MR. PARKER ON THE COMMON ROCK-LOBSTER. [Mar. 5, ments respecting them will possibly be more advantageously published as an appendix to the account of this bird which, as most (though apparently not every one) of our Members are aware, was drawn up more than twelve months ago, at the request of the Royal Society, by Mr. J. W . Clark and Mr. Edward Newton." Mr. T. J. Parker exhibited and made remarks upon the stridulating organ of the Common Rock-Lobster (Palinurus vulgaris). He stated that the apparatus in question was produced by a peculiar modification of the antennulary sternum and of the basicerite or second joint of the antenna. The antennulary sternum forms a projecting vertical keel, with a rounded anterior border, and slightly convex sides; the anterior border is grooved in the middle line, the groove being bounded on each side by a strong smooth ridge; each lateral surface is marked with a shallow groove; and between this groove and the border, to which it is parallel, the surface is so smooth as to have the texture of polished ivory. The basicerite is uncalcified along a slit-like space on its inner surface; this space is filled up with a thick chitinous membrane, which is produced superiorly into a large flap, projecting outwards from the surface of the joint. Immediately beneath this flap the chitin becomes thickened, takes on the form of an oval area or pad, about \ inch long by \ inch wide, and marked by a number of fine parallel ridges. In relation with the inferior edge of this pad is a small calcified tubercle. When the antenna is in place, the flap works over the ridge on the corresponding side of the anterior border of the antennulary sternum, the tubercle fits into the groove on its lateral surface, and the ridged pad is closely applied to the smooth space between the groove and the border. Under these circumstances, when the antenna is moved upwards the friction of the pad against the smooth surface produces a loud grating noise, the principle being similar to that of the sound produced by the friction of india-rubber against paper. The apparatus can at any time be thrown out of gear, and the antenna moved noiselessly, by slightly abducting the latter. In November last, Mr. Saville Kent remarked in * Nature' upon the " shrill squeaking sound" emitted by living specimens of Palinurus 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. He stated further that the apparatus was possessed by both sexes, although in the two specimens examined the noise produced was far louder in the male ; and he also remarked upon the fact that, notwithstanding the great perfection of the stridulating organ, the auditory organ of Palinurus is in a very imperfect condition. The following papers were read :- |