164 NEST-BUILDERS. 



producing the phenomena under consideration." * I beg to 

 put in a demurrer to this conclusion, until more decisive 

 proof is given me in the detection of an organ fitted to 

 make the snail a boring operative. 



A very few mollusks not endowed with the mechanical 

 power to bore and tunnel, and yet, as it were, conscious that 

 some extraneous covering would be useful to them, set about 

 to provide it each after its fashion. Thus the Phorus, 

 which is a genus of nomade Gasteropods, gathers together 

 the dead and living shells of other species, and intermingling 

 them with pieces of broken coral and small stones, glues 

 them to the outside of its shell so as to hide its true features 

 and make it pass as a dead mass of inorganic matter ; or, 

 as when the cemented shells are of the turreted kind, it may 

 frighten thus away an enemy, for the shells, pointing in all 

 directions, present to view an armature of strong spikes, on 

 which even a hungry fish might hesitate to feed. Some 

 Modiolae cover themselves with a hairy vestment made of 

 the threads of their byssus;j- and one native Crenella (C. 

 discors), " forms for itself a kind of nest or case by stitch- 

 ing together the small sea-weeds or corallines with its byssal 

 threads ; " J while another (C. marmorata) digs deep into 

 the leathery coat of Ascidia, and very effectively hides itself 

 there. The unmoving Gastrochaena modiolina is found on 

 the Guernsey shores, living in the crevices of rocks amidst 

 the debris of madrepores, and of shells and gravel ; and with 

 this material it puts together a sort of nest or chamber that 

 resembles a Florence flask, and completely encases the shell. 

 The outside of the nest is rough, but the inside is smooth, 

 and consists of thin layers of a calcareous secretion applied 

 by the animal, which leaves open the neck of the nest whence 

 it protrudes the tubes of respiration and of eflete matters. 

 The animal can, of covirse, enlarge the nest to suit its growth, 

 and it can also prolong the neck so as to keep it above any 

 overlying madrepores. § The Lima, whose active habits I 

 have had already occasion to notice, is also occasionally a nest- 



* Ann. and Mag. N. Hist. viii. 459. 



t Pliilippi thus describes the nest of his Modiola vestita : " InvohTcrum 

 mirabile sacci instar totam testam occultans, intus e tomento filorura cine- 

 reorum, extus e lapillis, conchyliornm fragmentis et similibus compositum 

 est, et cum parte postica cohferet, a cujus filis ex parte ortum videtur. 

 Byssum nullum inveni, eumque fugacem, a filis tenuissimis contextum fuisse 

 saccoque forte altera ex parte originem dedisse puto." — Mullusc. Sicil. ii. 

 51. 



X Alder in Trans. Tynes. Nat. Club, i. 1/5. 



§ Loudon's Mag. N. Hist,, vi. 404. All Gastrochrenae make similar 

 bottle-shaped cases. See Forbes and Hanley's Brit. MoUusca, i. 133. 



