METHODS OF ATTACK AND DEFENCE 99 



the rest of the Terebellids this worm has no tube, but creeps 

 about actively. It is bright red in colour, and has a number 

 of tentacles which on stimulation become brilliantly phos- 

 phorescent, and are coiled round the body in protective 

 fashion. When offered to certain fish in the aquarium 

 these worms were, after one or two trials, rejected by them. 

 Upon the tentacles being removed, however, the body was 

 attacked and eaten with relish. Evidently, then, some dis- 

 tasteful property is associated with the tentacles, and it is 

 their bright colour which enables the fish to recognise and 

 avoid them. 



Occasionally, it is interesting to note, the cause of the 

 unpalatability is also the cause of the conspicuousness, e.g. 

 uric acid. 



Crossland (191 1) concludes from the almost universal 

 occurrence of colour in the family of Chromodorids, and 

 from their habit of crawling about in the open, that the 

 bright colours have some protective value. Distastefulness 

 has been proved experimentally by trying to feed Chromo- 

 dorids to fishes. The fishes would not eat them though they 

 would swallow pieces of Margaritifera and Balistes which 

 had been soaked in formalin. Some would dash up to a 

 Chromodoris and then turn away after touching it. Others 

 went so far as to take the Chromodorids into their mouth, 

 but at once dropped them undamaged. 



On the flats of the coral reef at Little St. Cruz Island 

 (Philippines) Mortensen {op. cit.) remarks the presence of 

 shoals of a small fish, Plotosics anguillaris, which has a long, 

 pointed and barbed erect spine in each pectoral fin and a 

 similar one in the dorsal fin, all provided with poison glands. 

 The fishes, which are black with two longitudinal white 

 stripes on the sides of the back, swim in a close mass making 

 a large ball which seems to roll along over the corals, and is 

 exceedingly conspicuous. These balls can easily be caught 

 in a hand net. A fish when touched stuck to the fingers 

 and caused considerable and lasting pain. Singly, this fish 

 would not be conspicuous, hence the importance of the 

 gregarious habits. 



