72 PROTECTIVE COLORATION IN NUDIBRANCHS chap. 



is found by Professor Herdman to haunt no other situations 

 but 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 conspicuous Dendronotus arhorescens. 



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 

 observation 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 he an 

 unpalatable nettle in animal shape, but also to be conspicuous 

 enough to prevent its being experimented 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 pm-pose either of 

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

 edibility. These experiments, on the whole, 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, Ancula 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, 



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



