Haddon and Shackleton — A Revision of the British Actinice. 655 



terminal swelling, perforated. Coenencbiyme band-like, linear, adhering to 

 sponges ; polyps usually in linear groups of three or four, sometimes solitary. 



Colour. — Yellowish. 



Dimensions. — Height, 7 mm. ; diameter, 3 mm. ; tentacles, 5—10 mm. 



Habitat. — On various sponges, also on corallines and stones. Adriatic, 

 Marseilles, Naples. 



The foregoing description is compiled from the accounts given by Andres and 

 Carus. In the specimens we have examined, as sent out by the Naples Zoological 

 Station, we find that there is a considerable variation in the size of the polyps, 

 some attaining a height of 13 mm., and the coenenchyme forms an irregular 

 expansion on which the polyps are very crowded. The following anatomical 

 account is based upon these specimens. We leave it for others to determine 

 whether more than one species is commonly identified as P. axinellce. Koch's 

 specimens appear to be the same as ours, so far as his description and figures go. 

 The Adriatic specimens require re-investigation. 



Body -wall (PI. lix., fig. 8). — The body- wall is covered with a delicate 

 cuticle, beneath which lies a rather thin layer of continuous ectoderm. Numerous 

 oval nematocysts, which do not stain, are generally to be found among the 

 granular and deeply staining columnar cells of the ectoderm. Incrustations, 

 consisting for the most part of sponge spicules, are scattered, sometimes thickly, 

 sometimes more sparingly, through the mesogloea. Beneath these incrustations, 

 separated from the endoderm by a thin layer of mesogloea, lies an encircling 

 sinus, containing deeply staining nuclei and cell contents, as well as numerous 

 nematocysts similar to those which are found in the ectoderm. The sinus is 

 frequently interrupted by bars of mesogloea of variable thickness, so that in cross 

 section it often appears to consist of a circular series of rather narrow lacunae. 

 Canals frequently branch off from the sinus, and in many cases their connexion 

 with the ectoderm can be distinctly seen. Single isolated cells are occasionally 

 found enclosed in the mesogloea. The endoderm forms a very thin and almost 

 uniform layer. 



Sphincter muscle. — The sphincter muscle is, as described by Erdmann, diffuse 

 and endodermal. 



Disc and Tentacles. — There is nothing worthy of special note in the structure 

 of the disc and tentacles. 



(Esophagus. — The groove is well marked, and the mesogloea is considerably 

 thickened in this region (PL lx., fig. 6j. 



Mesenteries. — The arrangement of the mesenteries is macrocnemic. The 

 imperfect mesenteries are well developed, often reaching nearly half way from the 

 body -wall to the oesophagus. The longitudinal muscles are well developed in the 

 upper part of the mesenteries, close to the disc, the fibres being supported in this 



