112 A CHAPTER OF ACCIDENTS 



account of some of the more interesting among 

 them. 



On the submerged pinnacles of rock which one 

 here and there encounters along this part of the 

 coast, we found Madrepore corals growing ; not the 

 massive reef-forming species, but delicate encrusting 

 and arborescent forms like Dendrophyllia and Ccenop- 

 sammia. We also dredged in some abundance little 

 ''solitary" corals of the genera Hetej^ocyathus and 

 Heter op sammia : these corals are shaped something 

 like small thick disks, in the base of which there is 

 usually embedded and concealed a dead mollusk shell 

 which serves as a house for an active little Sipunculoid 

 worm. I kept some of these corals alive in my small 

 aquarium, and watched how their lodger-worm, by 

 thrusting out one end of its muscular body as a lever, 

 was able to whisk them about from place to place. It 

 is, in fact, as pretty an instance of commensalism, or 

 association for mutual benefit, as is known, and it 

 has attracted the attention of numerous naturalists. 



We noticed numerous other animal partnerships, 

 which might have been cases of commensalism, but 

 were more probably merely one-sided adaptations of 

 one animal standing in need of protection to another 

 animal capable of affording the required protection 

 without any expenditure of effort. For instance, a 

 very common branching zoophyte of this region is 

 Spongodes pustulosa (or some very closely related 



