TWO RARE BRITISH NUDIBRANCHS. 157 



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 posteriorly 

 directed one. The "erection" and movement of the papillae is 

 brought about in the same way by natural stimuli. These move- 

 ments led me to suspect the presence of cnidocysts. In spite, how- 

 ever, of the examination of the living animal and of sections of young- 

 specimens T 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 " cnidocystee nullse " as a diagnostic character. 



On some occasions I observed the peculiar lashing movements 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, while the rest of the 

 body was inverted. On another occasion it voluntarily loosened its 

 hold of the side of the glass vessel and progressed slightly by means of 

 these contractions. Again, after floating foot upwards for some time, 

 it would wriggle to the bottom and immediately gain a footing. 



My specimen was quiet during the day. In the morning I found 

 that it had crawled out of the dish where it had been placed over- 

 night. This was done constantly. During the three weeks that I 

 kept my specimen no spawn was deposited ; hence probably it was 

 immature. 



As regards the significance of these observations. Continual 

 changes of form in the pleuropodial papillae during life have been 

 noticed by Dr. Norman in his species, L. Hancocki.% The complete 

 similarity, however, both in characteristic form and power of co- 



* " Die Cladohepatischen Nudibranchien," Zool. Jahrbiicher, Bd. v. (1890). 



+ " First Eeport on Nudibranchs of Plymouth Sound," Journ. Mar. Biol. 

 Assoc, (n. s.) I. ii. 1889, p. 189. 



% Norman, Ann. & Mag. Nat. Hist. 1877, xr. p. 518. 



