202 



Zoophytes. 



On the Animals which force other living Animals to form a Houi. 

 for their protection. By John Edward Gray, Esq., F.R.S., &c. 



We are all aware that the Bernhard crab often takes possession of 

 an empty shell ; * also that certain worms, as the Sipunculus, fix 

 themselves in other shells, as the pelican's foot [Aporrhaias Pes-peli- 

 cant), or in a Dentaliiim, and by collecting together a little earth at 

 the entrance, construct for themselves a good habitation ; and that a 

 species of annelide often takes possession of the tube of Vermetus 

 cancellatus, and contracts the mouth of the shell so as to form a regu- 

 lar dome, leaving only a small hole the size of the parasite.f Some have 

 believed that the parasite induces the Vermetus to do this for it, at the 

 same time causing its own death ; and from the similarity of the struc- 

 ture of the shell, of the dome, and that of the tube, there appears to be 

 some ground for this idea, but the fact wants patient examination and 

 verification. 



It has not been so generally observed that some Crustacea, Cirri- 

 pedes, Mollusca and Vermes take advantage of the manner in which 

 corals, sponges, and other radiating animals grow, and the ease with 

 which they are induced to turn out of their usual course, to fix them- 

 selves on their surface, so as to cause the animals of these kinds on 

 which they have affixed themselves, to form a chamber for their! 

 protection. Indeed, this may be also said to be the case, although 

 done by exactly the contrary process, with some vertebrated ani- 

 mals, as for example the larger Cirripedes, as Coronula diadema,| 

 Tubicinella Balaenarum, &c. which affix themselves to the skin of the 

 different species of whales, manatees &c., and then, by the gradual 

 addition of new shelly matter to the lower surface of the valves of] 

 their shell, gradually sink themselves as they grow into the thick skin 

 of these animals, until the skin entirely protects them ; the result be- 

 ing similar to the attack of the Guinea-worm and other parasites, 

 although these animals first enter by a pierced wound, while the bar- 

 nacles above referred to only enter by causing the absorption of the 

 surface by pressure. 



The parasitic Cirripedes are so abundant on corals, that they have 

 been noticed by many authors, who have written or figured these pro- 

 ductions, yet they have not been generally understood. Linnaeus 



* Whether or not he previously devours its natural inhabitant is foreign to the pur- 

 pose of this communication. 



f^ Gray's ' Etchings of Mollusca,' t. riS, f. 3, the right hand figure is the parasitic] 

 worm, and the two left hand figures arc the proper animal of the shell. 



