380 Mr. F. W. Gamble on 



am aware none of the terms used hj previous authors on this 

 subject do justice to the form of the extended pleuropodial 

 papilla. The interest of the matter is increased by the fact 

 that tlie tips of the " calyx-sheath " have the same power of 

 contractility, and that their extended form agrees with that of 

 the dorsal papillae. The velar processes also when extended 

 are of a very definite shape (see figs. 1 and 2). 



On gently touching the centre of the right side of the 

 animal with a clean sable brush three events occurred almost 

 simultaneously ; the rhino])hores pi'eviously expanded were 

 sharply retracted within their sheaths ; the velar processes 

 were extended; and the dorsal papillaa of the right side, espe- 

 cially those near the point of the brash, were erected from a 

 previously oblique position, the large papillte markedly 

 directing their whitish tips towards the brush. The effect 

 might be almost said to be " bristling." The papillae of the 

 left side were only feebly affected. On repeating the experi- 

 ment at different points I found that when the stimulus is 

 applied just behind the rhino]jhoral sheath the large postero- 

 external sheath-papilla directed its tip obliquely backwards 

 towards the point of attack, the first primary pleuropodial 

 papilla directing its tip forwards. Several times I observed 

 a single fully-expanded papilla move independently in an 

 oblique plane from an anteriorly directed position to a poste- 

 riorly directed one. The " erection " and movement of the 

 papilla3 is brought about in the same way by natural stimuli. 

 These movements led me to suspect the presence of cnido- 

 cysts. In spite, however, of the examination of the living 

 animal and of sections of young specimens fV inch long (for 

 the use of which, together with help in many ways, I am 

 indebted to my friend j\Ir. Walter Garstang), I have hitherto 

 been unsuccessful ; indeed Bergh *, in his description of the 

 genus, has stated " cnidocystas nullaj " as a diagnostic cha- 

 racter. 



On some occasions I observed the peculiar lashing move- 

 ments of the whole body already noticed by Mr. Garstang f. 

 Tims, on pushing the animal laterally with a brush until its 

 foothold gave way, it bent upon itself and executed a series 

 of very vigorous S-shaped movements from side to side, the 

 ventral surface of the foot being kept at about the same 

 position on the surface of the water, the rest of the body 

 inverted downwards. On another occasion it voluntarily 



* " Die Cladohepatiscben Nudibraiicbien," Zool. Jahrbiiclier, Bit. v. 

 (1890). 



t " First Report on Niidibranobs of Plymoutb Sound," Journ. Mar. 

 Biol. Assoc, (n. s.) I. ii. 1869, p. 169. 



