NUDIBRANCHIATA. 23 



N. H. ii. p. 311)^ ^^ At iiiglit_, especially when thus in 

 motion^ it appeared most brilliantly phosphorescent ; 

 the light flashing progressively but very rapidly along 

 the body, especially from all the branchial tufts and the 

 edges of the veil and crest/' The Nudibranchs are 

 very sensitive to external influences, shrinking quickly 

 from contact, and withdrawing their organs on the 

 slightest apprehension of danger. When crawling on 

 seaweeds or corallines, they often detach themselves on 

 being disturbed, and drop to the bottom of the water. 

 The Eolides, when alarmed or irritated, erect their 

 papillae, and sometimes agitate them in a convulsive 

 manner, directing the points to any source of annoyance, 

 each papilla being endowed with a motion independently 

 of the rest. On such occasions urticating filaments are 

 probably ejected from the tips of these organs. Alder 

 and Hancock once observed minute streams of a milk- 

 white fluid (which they believed to be of a stinging 

 nature) emitted from the papillae of Eolis picta. The 

 papillae of Eolis and several allied genera are very 

 slightly attached to the back ; and the animal seems to 

 have the power of casting them off voluntarily, in the 

 same way that a crab throws off its claws or a starfish 

 its arms. The papillae, when cast off, swim through 

 the water, like worms, propelled by the \dbratile cilia, 

 and occasionally by a spasmodic action of the muscles. 

 They are quickly reproduced, if the animal is in a 

 healthy state ; and in the meantime it does not appear 

 to suffer any inconvenience from the want of these 

 organs, crawling about in perfect unconcern. For this 

 reason Mr. Couthouy conjectm-ed that the so-called 

 branchial processes are not true respiratory organs, but 

 that this function was chiefly performed by the skin in 

 all the Nudibranchs, The separation of Eolis and a 



