PEDICELLIN^E I PEDICELLINA. 383 



determine.* The tentacula are about one-third the length of the 

 head of the polypus, and are about sixteen in number, tuberculated, 

 and thickly ciliated, as is also the interior of the whole line of the 

 alimentary canal. Near the junction of the stomach and ascending 

 rectum, and contained within them, a small dark body may often be 

 observed in active rotatory movement ; the nature of the body, which 

 has been noticed in some other zoophytes, and the cause of its mo- 

 tion, have not, I believe, been fully understood : it is nothing more 

 than faecal matter kept in constant rotation by the action of the cilia 

 lining the whole internal surface of the alimentary canal, and which, 

 by their peculiar arrangement, drive it on towards the place by which 

 it is to make its exit thus supplying the office of proper propelling 

 muscles. The polypi are usually non-symmetrical, one side being 

 more bulged out than the other, but they are capable of assuming 

 various other forms and appearances. The tentacula, too, vary much 

 in their disposition, being sometimes directed either upwards or out- 

 wards ; at others they are curved inwards, usually to a small extent, 

 but occasionally so much so as to be entirely lost to view, being con- 

 cealed by the outer tunic of the polypus. The motions of the polypi 

 of this species are very lively and peculiar. All the Ascidian zoo- 

 phytes are much more vivacious and active in their movements than 

 the Hydroid, and this is the necessary result of their higher organ- 

 ization." 



Mr. Lister's description of this zoophyte is as follows : 

 " It consists of a creeping tube and a number of stems branching 

 from it, each ending in an animal that is shown (not very distinctly) 

 at fig. 42, d. The stems, though commonly still, have free power 

 of motion ; and when one is disturbed it bends quickly to and fro, so 

 as to strike one or two more; these again strike upon others, and 

 thus for a few seconds all are in action : but they soon return to 

 quietness, and the arms, which during the commotion had been 

 doubled in, open again. 



" The arms are placed on the edge of a pretty transparent tunic, 

 and have granulations on their back. They are fringed with cilise 

 possessing the same action as those of Ascidise and Flustrae; and in 

 the specimen drawn, small substances were occasionally seen carried 

 downwards along them. As in Flustra, a part of the intestine had 

 within it a revolution of particles and dark matter round its axis, 

 and this part communicated with an ascending rectum. The arms 

 at the part of the circle opposite to the rectum appeared to be con- 

 * Van Beneden says that this is the generative system. 



