The reef itself has no passage of colour but is imitated by some shell.Purple and red and white,and green and yellow,pied and striped and clouded,the living shells wear in every combination the livery of the dead reef -if the reef be dead -so that the eye is continually baffled and the collector continually deceived.Ihave taken shells for stones and stones for shells,the one as often as the other.A prevailing character of the coral is to be dotted with small spots of red,and it is wonderful how many varieties of shell have adopted the same fashion and donned the disguise of the red spot.A shell I had found in plenty in the Marquesas I found here also unchanged in all things else,but there were the red spots.A lively little crab wore the same markings.
The case of the hermit or soldier crab was more conclusive,being the result of conscious choice.This nasty little wrecker,scavenger,and squatter has learned the value of a spotted house;so it be of the right colour he will choose the smallest shard,tuck himself in a mere corner of a broken whorl,and go about the world half naked;but I never found him in this imperfect armour unless it was marked with the red spot.
Some two hundred yards distant is the beach of the lagoon.Collect the shells from each,set them side by side,and you would suppose they came from different hemispheres;the one so pale,the other so brilliant;the one prevalently white,the other of a score of hues,and infected with the scarlet spot like a disease.This seems the more strange,since the hermit crabs pass and repass the island,and I have met them by the Residency well,which is about central,journeying either way.Without doubt many of the shells in the lagoon are dead.But why are they dead?Without doubt the living shells have a very different background set for imitation.But why are these so different?We are only on the threshold of the mysteries.