ACTINIAD^ : ADAMSIA. 209 



to which the Actinia is attached covers, for the most part, nearly the 

 whole of the external surface of the old shell to which it is fixed, 

 and from the circumference of its aperture, is prolonged into a 

 large hollow expansion, resembling in form, and occupying, rela- 

 tively to the shell, the place of a ventricose body-whorl. Its sub- 

 stance is of a uniform thickness throughout its whole extent, of a 

 greenish-brown colour, translucent, having both surfaces irregularly 

 wrinkled transversely. In a recent state it is quite flexible, but 

 when dried it is brittle. It takes fire and burns readily, leaving a 

 very small residuum, which does not effervesce with acids. It is 

 insoluble in boiling water and in alcohol, but dissolves slowly in 

 acids, and in solutions of the alkalies. Its general appearance may 

 be compared to that of the cases of Tubularia indivisa, except in 

 point of colour." 



" The case thus formed by the old shell and the horny membrane, 

 and covered by the Actinia, I have always found inhabited by a 



variety of the hermit-crab." " Its natural history is perhaps 



doubtful. Is the horny case secreted by the Actinia 1 Or is it the 

 dead axis of some zoophyte, like that which covers old Buccina 

 (Alcyonium echinatum, Flem.), and which I have found forming an 

 extension of the body-whorl of the Turbo littoreus, also inhabited 

 by the Pagurus ] Or, is it likely that the old shell, with a young 

 crab in it, may have been swallowed by the Actinia ; that the crab 

 may have forced its way through the walls of the stomach and the 

 integuments of the latter, and that the Actinia then secreting 

 a peculiar membrane to defend its base, the crab may have found 

 itself provided with a habitation suited to its wants 1 To this last 

 supposition an objection is found in the fact, that the full-grown 

 shell of Trochus Magus forms sometimes the base of the horny case, 

 and this shell is too large to enter the mouth of the Actinia. It 

 seems to be probable that the horny membrane is produced by the 

 Actinia ; and that its formation presents a striking instance of the 

 operation of that beautiful law of Nature which makes the habits of 

 one animal subservient to the wants of another."* 



* " Many naturalists," says the Rev. D. Landsborough, " have observed that there 

 seems to be a treaty of union betwixt the hermit-crab and the spotted seoranemone 

 {Actinia maculuta). I lately kept one of these pretty sea-cmemoncs for some days in 

 sea- water ; it had fastened itself to a little fragment of a screw-shell {Tiirritdlu), but 

 its co-tenant in the inside was not a hermit-crab, but a pretty red annelide. Be this 

 as it may. certain it is that, on this occasion, we found that the spotted anemone had 

 fastened itself to the outer lip of many of the large roaring liwkies {Bticcinum un- 

 dattim) brought up, and wherever there was an anemone without, there we found a 



P 



