72 PROTECTIVE COLORATION IN NUDIBRANCHS chap. 



the under side of stones and overhanging ledges of rock which 

 are colonised by a hydroid, known as Clava multicornis. The 

 Doto is masked by the tentacles and clusters of sporosacs on the 

 zoophyte, with whose colouring and size its own cerata singularly 

 correspond. A similar and even more deceptive correspondence 

 with environment was noticed in the case of the very conspicu- 

 ous Dendronotus arborescens. 



In these cases, the colouring and general shape of the cerata 

 are protective, i.e. they match their surroundings in such a way 

 as to enable the animal, in all probability, to escape the observa- 

 tion of its enemies. According to Professor Herdman, however, 

 the brilliant and showy coloration of the cerata of Aeolis is not 

 protective but ' warning.' Aeolis does not hide itself away as if 

 shunning observation, like Doto^ Tritonia, and Dendronotus ; on 

 the contrary, it seems perfectly fearless and indifferent to being 

 noticed. Its cerata are provided with sting-cells, like those of 

 Coelenterata, at their tips, and its very conspicuousness is a 

 warning to its enemies that they had better not try to attack 

 it, just as the showy white tail of the skunk acts as a sort of 

 danger-signal to its own particular foes. It is important for the 

 Aeolis^ not merely to be an unpalatable nettle in animal shape, 

 but also to be conspicuous enough to prevent its being experi- 

 mented upon as an article of food, in mistake for something less 

 nasty. 



Professor Herdman subsequently conducted some experi- 

 ments ^ with fishes, with the view of testing his theory that the 

 shapes and colours of Nudibranchs serve the purpose either of 

 protection or warning, and bear direct relation to the creature's 

 edibility. These experiments, on the Avhole, distinctly tended 

 to confirm the theory. Aeolis was evidently very nasty, and 

 probably stung the mouths of the fishes who tried it. For the 

 complete success of the theory, they ought to have let it severely 

 alone, but the fish were evidently accustomed to make a dash 

 at anything that was dropped into their tank. Another con- 

 spicuous mollusc, A^icida cristata., was introduced. Professor 

 Herdman and his collaborator each commencing operations by 

 eating a live specimen themselves. They found the taste 

 pleasant, distinctly like that of an oyster. The fish, however, 



1 A detailed account is given in Proc. Liverp. Biol. Soc. iv. (1890) pp. 150-163. 



