52 GENUS CERAPUS. 



5i\habitant, and appears to invest it closely, nevertheless 

 when an impediment is presented, m consequence of 

 which the animal is prevented from proceeding onwards, 

 he turns his body immediately, and apparently without 

 ^any difficulty within the tube, protrudes his head 

 from the opposite extremity, and thus makes use of either 

 end indifferently as the anterior part. 



When swimming about one half of the body is pro. 

 jected from the tube, and is suddenly and repeatedly in- 

 flected, so as to proceed forwards by jerks. It very much 

 resembles, at first view, the larvae of insects of the family 

 of Phr} ganides, for which it nmst have been hitherio 

 mistaken. 



Not having the tube before me, I can only say from 

 recollection, that it is c}lindric, membranaceous, dia- 

 phanous, open at each end, and of a colour somewhat 

 reddish; but of its origin I know nothing, a little obser- 

 vation on the spot might however determine this. To sup- 

 pose it fabricated by the animal, would be supposing an 

 absolute anomaly in the history of the whole race of crabs, 

 and there is no organ belonging to the Cerapus which 

 could be adapted to a function so remarkable. I think 

 it probable the tube will be ascertained, by further and 

 more particular examination, to have been constructed by 

 one of the annelides; indeed it perfectly resembles in 

 every respect a section of the tube of that species of Tu- 

 bularia which we so commonly find in the cavities of the 

 large Alcyonium of our coast. 



A plnte of this animal, with the necessary details, will 

 be given in the succeeding number. 



