10 INTRODUCTION. 



CHAPTER II. 



OF THE ANIMALS WHICH INHABIT SHELLS. 



OF these animals a minute and accurate anatomical de- 

 scription is not to be expected; for little more is known 

 of their structure than what has been given by natur- 

 alists concerning their external characters. 



Some of the animals which inhabit shells, are also found 

 in the mollusca state; that is, without any testaceous co- 

 vering. Such, for instance, is the Limax, or snail. 



The animals which have been described as inhabiting 

 shells are the following; viz. Doris, Triton, Ascidia, Tc- 

 thys, Limax, Spio, Amphitrite, Terebella, Nereis, Sepia, 

 and Clio. 



Doris, — The body is creeping, oblong, and flat beneath; 

 the mouth is placed below on the forepart; vent behind 

 on the back, and surrounded by a fringe. Feelers two or 

 four, situated on the upper part of the body in front, and 

 retractile within the proper receptacles. — The animal 

 which inhabits the Chiton belongs to this genus. 



Triton. — The body is oblong, and the mouth is furnish- 

 ed with an involute spiral proboscis ; tentacula or arms 

 twelve, six on each side, divided nearly to the base. The 

 hind ones cheliforous. — ^TheTriton inhabits different spe- 

 cies of Lepas. 



Ascidia. — The body is fixed, roundish, and apparently 

 issuing from a sheath; apertures two, generally placed 

 near the upper end, one beneath the other. The animals 



