Alcyonella. Z. ASCIDIOIDA. 317 



ter of an inch in breadth or diameter. This case being very trans • 

 parent, all the motions of its inhabitants may be discerned through 

 it distinctly. It seems divided internally into several apartments, or 

 rather to contain several smaller Sacculi, each of which encloses one 

 of these animals. The openings at the tops of these Sacculi are but 

 just sufficient to admit the creature's head, and a very small part of 

 its body, to be thrust out beyond them, the rest remaining always in 

 the case. The animal can, however, when it pleases, draw itself en- 

 tirely down within the case, which is an asylum to secure it from its 

 enemies, (for it is not unlikely many of the larger aquatic insects prey 

 upon it,) and a safe and agreeable retirement wherein to perform the 

 functions of digestion, sleep, and the other necessary calls of nature. 

 This case it can, I say, retire into at pleasure ; and it never fails to 

 do so when any sudden motion of the water or of the vessel it is in dis- 

 turbs it : as also when it has seized with its arms any of the minute 

 insects which serve for its food. 



" The arms are set round the head to the number of forty, 

 having each the figure of a long^ one of whose hooked ends is 

 fastened to the head ; and all together when expanded compose a 

 figure somewhat of a horse-shoe shape, convex on the side next 

 the body, but gradually opening and turning outwards, so as to 

 leave a considerable area within the outer extremities of the arras. 

 And when thus extended, by giving them a vibrating motion, the 

 creature can produce a current in the water, which brings the ani- 

 malcules, or whatever other minute bodies are not beyond the sphere 

 of its action, with great velocity to its mouth, whose situation 

 is between the arms : where they are taken in if liked, or else by a 

 contrary current, which the creature can excite, they are carried away 

 again : whilst at the same time other minute animalcules or substan- 

 ces, that by lying^without-side the inclosure made by the arms are 

 less subject to the force of the stream, are frequently seized by them : 

 for their sense of feeling is so exquisite, that on being touched ever 

 so slightly by any such little body, it is caught immediately and con- 

 veyed to the mouth. However, one may observe the creature is 

 sometimes disappointed in its acquisition, for after drawing down one 

 of the arms suddenly inwards towards the mouth, it may be perceiv- 

 ed slowly extending itself again without the creature's retiring into 

 its case ; which it fails not to do on meeting with anything worth 



the while. 



" The food is conveyed immediately from the mouth cr opening 

 between the arms, through a very narrow neck, into a passage seem- 

 ingly correspondent to the oesophagus in land animals ; down which 



