442 MR. T. J. PARKER ON PALINURUS VULGARIS. [May 7, 



1. Note on the Stridulating Organ of Palinurus vulgaris. 

 By T. Jeffery Parker, Assoc. R.S.M. 



[Received March 27, 1878.] 



(Plate XXX.) 



On the 5th of March I exhibited to the Society a structure, 

 evidently of the nature of a stridulating organ, which I had found 

 in the common Palinurus, and which I then believed had hitherto 

 escaped notice. On the following clay, however, Professor Huxley 

 showed me a reference, which he had that morning chanced to meet 

 with, to a paper by Dr. Karl Mobius, in the ' Archiv fur Naturge- 

 schichte' for 1867, the title of which, " Ueber die Entstehung der 

 Tone welche Palinurus vulgaris mit den ausseren Fiihlern hervor- 

 bringt," showed at once that I had been anticipated. I hasten, 

 therefore, to render to Dr. Mobius such credit as belongs to the 

 discovery, and take the opportunity, at the same time, of making 

 some criticisms on his paper, as well as a few additional remarks 

 upon the organ in question 1 . 



The main anatomical features of the stridulating organ are described 

 by Mobius, as they could hardly fail to be, with perfect correctness. 

 He fails, however, to notice either the guiding tubercle (Plate XXX. 

 figs. 3 and 4, t) , situated just below the ridged pad ( p) on the antenna, 

 or the groove for its reception on the antennulary sternum (fig. l,g): 

 the formei, indeed, is shown in his figure; but no reference is made 

 to it. As I mentioned in my former communication, these structures 

 are of great importance, as by their means the apparatus is brought 

 into gear : when the tubercle does not fit into the groove the pad is 

 no longer in close apposition with the smooth surface of the anten- 

 nulary sternum, and the antenna moves noiselessly. 



As to the functions of the various parts of the apparatus, the 

 account given by Mobius is altogether at variance with my own. 

 He makes the observation that the lower surface of the flap (figs. 

 1-4,/) which plays over the lateral ridge (figs. 1 and 2, r) of the anten- 

 nulary sternum is beset with innumerable close-set minute hairs, 

 inclined with their points upwards, and that, corresponding to these, 

 fine scratches are to be seen on the surface of the ridge itself. All 

 this is perfectly correct : there is no doubt about the presence or 

 the direction of the hairs ; and the scratches are quite visible with a 

 hand lens. But Mobius goes on to say that the scratches are pro- 

 duced by the hairs, and that it is the friction of the flap against the 

 smooth edge of the antennulary sternum which produces the sound, 

 by the upwardly directed hairs catching against the surface, when 

 the antenna is moved in the same direction. Of course when the 

 antenna moves downwards the hairs will lie flat and present no ob- 



1 I find that Leach, in his ' Malacostraca Podophthalmata Britanniae' 

 (1815), mentions the stridulating of Palinurus, and correctly ascribes the sound 

 to the friction of the antenna against the "clypeus" (antennulary sternum). 

 He gives, however, no description or figure of the apparatus. 





