FORM REGULATION IN CERIANTHUS. 24! 



the exit of water. In the expanded condition the disc possesses 

 the form of a broad shallow funnel extending from the base of 

 the marginal tentacles to the margin of the mouth and continued 

 aborally in the oesophagus. The mouth is slit-like in form with 

 one siphonoglyph or gonidial groove at one end of the slit. 

 The disc is marked with radiating lines, slightly depressed, which 

 correspond to the lines of attachment of the mesenteries beneath 

 the surface : these continue aborally in the oesophagus. The 

 oesophagus extends aborally from the disc about -* 1 the length 

 of the body when the animal is fully extended. 



The marginal tentacles, as their name implies, are borne upon 

 the margin of the disc, usually in about three rows, the number 

 varying in grown specimens from about 41 to 71. About the 

 margins of the mouth are the shorter labial tentacles which are 

 fewer in number than the marginal tentacles, and form only a 

 single circle. 



The body appears brownish in color, but upon close examina- 

 tion is found to be marked with light longitudinal stripes or lines 

 of varying width, some of which extend the whole length of the 

 body while others are shorter. These are in reality merely 

 unpigmented areas between the stripes of brown pigment. The 

 color of the marginal tentacles is in general effect lighter than 

 that of the body, but they are marked by transverse bands of 

 dark pigment. The labial tentacles are brownish and usually 

 unstriped. The disc and oesophagus in large, apparently old 

 specimens are dark brown without definite striping. 



As regards the internal anatomy certain points are of interest 

 in this connection. It has long been known that the arrange- 

 ment of the mesenteries in the Cerianthidse differs in some re- 

 spects from that in the other Actinozoa. In the cesophageal 

 region all mesenteries extend from the body-wall to the oesopha- 

 gus and thus divide the enteron of this region into a series of 

 longitudinal radiating chambers which open into the enteron 

 aborally. At the oral end each of these intermesenterial cham- 

 bers opens into the cavity of a single marginal tentacle ; thus 

 the marginal tentacles are always equal in number to the inter- 

 mesenterial chambers. The labial tentacles, while corresponding 

 in position to intermesenterial chambers, are fewer in number. 



