452 



PHORONIS 



occupied tubes are found to show that, under ordinary circum- 

 stances, a living Cerianthus occupies the interior of the tul 

 and a community of Phoronis live in its wall. This species o\ 

 Phoronis is never found anywhere else, and the species of Ceri- 

 anthus is very rarely found without the Phoronis" 



Ph. austrcdis is sluggish in its movements, but other specie 

 are capable of very active movement, and withdraw theh 



heads in a moment at the approacl 

 of danger. A Neapolitan species 

 Ph. Jcowalevskii known to the fisher- 

 men of that place as " Ficchetelli 

 bianchi " or " Vermi di ceppa " lives 

 chiefly on submarine posts and piles ; 

 its tubes, closely interlacing, for] 

 a dense feltwork, upon which Asei- 

 dians and Sea-anemones often settle, 

 and over which Ophiurids and Poly- 

 Fig.227. A piece of a colony of pa. chaets creep. The tubes of thi 



psammophila Cori Slightly ieg are rendered opaque by tilt 



magnified. The tubes are r ^ r u / 



covered by particles of sand, excreta ejected from the body, aii( 



small shells, etc. ^ do n()t afctach foreign substanc 



to the outside to anything like the same degree as Ph. psammo- 

 p>hila, which live in sandy places, and are termed by the Siciliai 

 fishermen " Tubi di sabbia." The feltwork of Ph. kowalevskii 

 attains a thickness of 5 to 8 cm. In each case the tube is mucl 

 longer than the animal it shelters, and is so entangled with its 

 neighbours, to which it frequently adheres, that it is a mattei 

 of considerable difficulty to isolate it. 



The various species of Phoronis differ a good deal in size 

 Cori gives the average length as varying from 1*5 to 7*9 mi 

 in Ph. hippocrepia and up to 127 mm. (6 inches) in Ph. australii 

 Probably the very short individuals of the first-named species 

 had not attained their adult stature. Ph. australis has recently 

 formed the subject of a memoir by Dr. W. B. Benham, 1 from 

 whom the following account is mainly taken. 



The length of the individuals varied from three to six inches, 

 and their diameter, which is not very uniform, averaged one- 

 eighth of an inch. At one end, which, since it bears the mouth, 

 we may call the oral end, is the very characteristic tentacular 



1 Quart. J. Micr. Sci. vol. xxx. 1890, p. 125. 



