fl& Zoological Collections. Invertebrata. 



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 eftervesce with acids. It is insoluble in boiling water and in alcohol, 

 but dissolves slowly in acids, and in solutions of the alkalies. Its general ap- 

 pearance may be compared to that of the cases of Tubularia irtdivisa, except in 

 point of colour. 



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

 the Actinea, I have always found inhabited by a variety of the hermit-crab {Pa~ 

 gurus Bernhardus,) differing from the common one in having the distal extre- 

 mities of the hands nearly smooth, and the margins of all the legs fringed with 

 hairs. The crab is so imperfectly covered by the case, tliat the whole anterior 

 half of tlie thorax remains exposed, even when the animal retires within it as much 

 as possible. 



"This curious combination of animals occurred to me several times in Rothesay 

 and Kames Bays, in Bute, either thrown ashore after easterly gales, or drawn in 

 by flounder-nets. Its natural history is perhaps doubtful. Is the horny case 

 secreted by the Actinea ? Or is it the dead axis of some zoophyte, like that which 

 covers old Buccina, {Alcyonium echinatum, Fl.) and which I have found form- 

 ing an extension of the body-whorl of the Turbo littoreus, also inhabited by the 

 Pagurus ?" " It seems to me 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." 



Another, and perhaps a still more remarkable, case of a similar adaptation is 

 also recorded by Dr. Coldstream, in the Halichondria suberica, (Flem. Brit. An. 

 522.) of which he found two specimens in Rothesay Bay, attached to old shells 

 of Turritella terebra, each containing within its mass a spiral cavity of two turns, 

 continuous with that of the shell. The cavity enlarges towards its mouth, so that 

 the outline of the whole mass is conical, and resembles that of some Buccina. 

 This cavity was inhabited, in both specimens found, by the common hermit-crab. 

 " Their history," says Dr. Coldstream, " I presume to be this. The crab 

 takes possession of the Turritella, when young ; the sponge then attaches itself 

 to the shell, and, as it grows, is forced, by the motions of the crab, to assume a 

 spiral form, with a cavity enlarging towards the mouth, corresponding to the 

 progressive development of its crustaceous inhabitant. 



" Montagu, who first described this species, found it generally in the very same 

 circumstances as those I have just described ; but he says that, in every specimen 

 which he obtained, the sponge had spread within the aperture of the old shell to 

 which it was attached ; and that, in some cases, it seemed to have increased so 

 much internally, notwithstanding the motions of the crab, as to force the latter 

 to remove to another shell (Wern. Mem. ii. 102.) In my specimens, the sponge 

 does not spread within the aperture of the shell — Ed. New Phil. Journ. Oct. 

 1830, p. 235. 



A similar observation had been previously made by M. Rapp, and noticed in 

 the work before quoted, (p. 26.) respecting the Alcyonium domuncula, Olivi, 

 {Zool. Adriatica, p. 241.) another of the sponges. " I have found this sponge," 

 says M. Rapp, " on the coast of Languedoc, always forming a thick and almost 

 cartilaginous, orange-coloured covering upon worn shells of moUusca, as Nerita, 

 Cerithium, Murex, in which a hermit-crab {Pagurus striatus) had taken up its 

 abode. This thick mass of sponge forms a continuation of the whorl of the shell, 

 and thus makes up the greater part of the dwelling of the crab." 



We think it right to remark that the observations of Dr. Coldstream on the 

 habits of these animals were purely original on his part, and that we consider it 

 to be no detraction from their value that the same facts have fallen under the ob- 

 servation of naturalists in other countries. Indeed we feel ourselves justified in 

 referring to the whole of Dr. Coldstream's paper, entitled " Additions to the 

 Natural History of British Animals," the greater portion of which will be found 



