1878.] MR. T. J. PARKKR ON PALINTJRUS VULGARIS. 443 



struction ; and in this way Mobius attempts to account for the fact 

 that no sound accompanies a downward movement. 



As to the first of these statements, one finds it rather hard to 

 believe that hairs so fine 1 that the surface they cover has a texture 

 like that of satin, can produce visible scratches ; their effect, one 

 would rather think, would be to impart a fine polish. I should be 

 inclined to suspect that the scratches must be due to fine particles 

 of sand getting in between the flap and the ridge. 



With regard to the second statement, that it is the friction of the 

 flap, and not that of the pad, which produces the sound, I can only 

 say that I have removed the flap entirely without any sensible dimi- 

 nution 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. 



It is not easy to see how such a mistake can have arisen ; but 

 Dr. Mobius's language is sufficiently explicit to leave no doubt of 

 his meaning. He says : — " Das gefurchte Feld [the ridged pad] 

 bringt keinen Ton hervor, wenn es iiber die Flache des Keiles 

 [the antennulary sternum] gleitet. Es leistet aber Widerstand gegen 

 die riickwarts gedrangten Haare, da es dicker und steifer als das 

 behaarte Feld [the flap] ist. Ausserdem geben seine Riefen dem 

 Gange der ganzen Platte grossere Sicherheit, da sie diejenige Rich- 

 tung haben, in welcher die Bewegungen ausgefiihrt werden." 



The fact that a downward movement of the antenna gives rise to 

 no sound seems to me to be explained by the mode of attachment 

 of the pad. It is connected by its inferior edge (figs. 4 and 5, i i) 

 with the lower boundary (fig. 5*, b') of the slit or uncalcified portion 

 of the basicerite, while at its superior edge it passes insensibly into 

 the inner wall of the soft flap. The outer wall of the flap, again, is 

 connected with the upper edge (fig. 5, b) of the slit in the basicerite. 

 Thus, while the pad is immovably fixed at its inferior edge, it is 

 capable of a considerable amount of displacement in the rest of its 

 extent ; and when pressed upon, by the downward movement of the 

 antenna, in the direction from y to x (fig. 4), it is forced inwards 

 upon the yielding tissue which underlies it, and never comes into 

 sufficiently close contact with the opposing surface to produce a 

 sound (fig. 5, A). But when it is pressed upon, in consequence of 

 the upward movement of the antenna, in the direction from x to y, 

 the only effect of the pressure is to cause it to bulge out oyer the 

 line of attachment ii, and so come into closer contact with the 

 opposing surface the stronger the force applied (fig. 5, B). 



In the matter of histological structure, the pad does not differ 

 from other chitinous membranes, being formed of fine superposed 

 horizontal laminse, marked by a vertical striation (fig. 5). It is, bow- 

 ever, of unusual thickness ; and its horizontal laminae have, for some 

 1 They arc not more than one S teven-hu ndredth of an inch in length. 



