THIO MOLTHOLOGY OF THE CHEILOSTOMATA. 315 



apex of tlie group pointing to the mediau poi-e. Round the 

 edge of the zooeciuin is a single line of pores. This arrange- 

 ment is constant in my Neapolitan specimens. The communi- 

 cation pores open into '' pore-chambers '' (29. c), as pointed 

 out by Levinsen (1891, pp. 250, 285).i 



The compensation-sac (c. s.) is thin-walled, its outline being 

 somewhat heart-sliaped when seen from the basal surface. 

 The median pore opens into it considerably on the proximal 

 side of its distal margin, a triangular bay {corn.) of the 

 body-cavity indenting the membrane of the compensation-sac 

 in the immediate neighbourhood of the frontal surface. The 

 parietal muscles {jh m.) are strong, and are arranged in 

 distinct groups. 



The function of the median pore in M. malusii has fre- 

 quently been discussed, and my results do not agree with 

 those of any of my predecessors. Jullien (1888, 4, pp. 

 36, 39) gives the name " fenestrula '^ to the median pore, 

 which he describes as forming the narrow end of a funnel 

 C' cornicula"), the other end of which opens into the tentacle 

 sheath. Jullien figures the cornicula in pi. xv, fig. 2, from 

 Avhich it appears to me clear that the funnel is the part of the 

 body-cavity which I have described above (fig. 63, com.) as 

 indenting the distal outline of the compensation-sac. 



Pergens (1889, p. 507) does not believe in the existence of 

 Jullien's compensation-sac, and describes the diaphragm or 

 vestibule as opening into the body-cavity and not into the 

 tentacle sheath. 



The commonly received opinion that the vestibule is 

 traversed by the tentacles during their protrusion is, 

 however, based on too many observations to be lightly 

 dismissed. 



Pergens further states (p. 506) that the median pore of 

 M. malusii opens into the body-cavity. The 'Mongitudinal 

 muscles " mentioned by him were probably parietal muscles, 

 while I suspect that the appearance of a " sack " between 



1 For the pore-chambers of Clieilostomafa see also Waters (1898), 

 p. 658. 



