380 Mr. F. W. Gamble on 
am aware none of the terms used by 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 the 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 rhinophores previously expanded were 
sharply retracted within their sheaths; the velar processes 
were extended; and the dorsal papille of the right side, espe- 
cially those near the point of the brush, were erected from a 
previously oblique position, the large papille markedly 
directing their whitish tips towards the brush. The effect 
might be almost said to be “ bristling.” The papilla 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 rhinophoral 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 
papille is brought about in the same way by natural stimuli. 
These movements led me to suspect the presence of enido- 
cysts. In spite, however, of the examination of the living 
animal and of sections of young specimens 3°; inch long (for 
the use of which, together with help in many ways, I am 
indebted to my friend Mr. Walter Garstang), I have hitherto 
been unsuccessful; indeed Bergh *, in his description of the 
genus, has stated “ cnidocyste nulle” 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. 
Thus, 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 Cladohepatischen Nudibranchien,” Zool. Jahrbiicher, Bd. v. 
(1890). 
+ “First Report on Nudibranchs of Plymouth Sound,” Journ. Mar, 
Biol. Assoc, (n. s.) I. ii, 1889, p, 189. 
One oe 
