18 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 naturalists 

 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 slug. 



The animals which have been described as inhabiting 

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

 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 fore part; 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. 



Ti-'itoti. — 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 

 hinder ones cheliferous. — The Triton inhabits diiferent 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 

 are found in the sea, and adhere by their base to rocks, 



