258 LIFE BY THE SEASHORE. 



some shade of red-brown, beautifully streaked and marbled 

 with white; the processes are also red or crimson, the 

 colour fading towards their tips as it does in most seaweeds. 

 The animals are very active, continually creeping and twist- 

 ing about. The eggs are yellowish in colour, and are laid 

 in a close spiral with very narrow coils. I kept a pair in 

 confinement for a long time, but rashly introduced a sea- 

 anemone (Actinoloba dianthus) into their aquarium. In 

 the course of their travels the sea-slugs crawled over part 

 of the anemone, and it forthwith discharged its stinging- 

 threads and killed the sea-slugs. They were not eaten, 

 being, indeed, almost as large as the anemone, but simply 

 killed, much to my sorrow, for they were beautiful pets. 



It has been supposed that it is an important part of the 

 function of the branched papillae that they render Dendro- 

 notus and its allies inedible ; but I can hardly believe that 

 this is the whole explanation, for forms like Ancula cristata, 

 which have relatively few papillae and no brilliancy of 

 colour, are also severely let alone by most animals. The 

 aquarium in which the Dendronotus lived afforded some 

 interesting results as to relative immunity to attack. Its 

 chief occupant was a young Norway lobster of beautiful tint 

 and large appetite, not very easy to satisfy. It was fondest 

 of shrimps, prawns, and young crabs of various kinds, but 

 had a way of eating these rather trying to the feelings 

 of the onlooker, so I liberally supplied it with various sea- 

 slugs, of which at the time I had a large stock. Colourless 

 specimens of Ancula cristata, small Dorids, Dendronotus, 

 and others, which seemed less alive than crabs and quite 

 suited to the lobster's taste, were placed in his dish. But 

 though the coat of a young spider-crab was no protection 

 against the voracity of the Nephrops, the delicate sea-slugs 

 crawled untouched over his body, while he seemed only 

 anxious to get out of their way. When the anemone came 

 on the scene, however, the conditions were largely reversed. 

 The crabs seemed able to resist its deadly power to a much 

 greater extent than the defenceless sea -slugs, who fell 

 victims at once; but in natural conditions the sea-slugs 

 rarely live in those dark and dank localities which suit this 

 particular anemone. The experiment showed in an interest- 

 ing way that the value of a protective device depends upon 



