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



Cell enclosures. — Large ectodermal canals, penetrating the mesogloea, are very 

 characteristic of the genus Zoanthus ; they also occur in Parazoanthus. In 

 Z. coppingeri there are numerous large anastomosing canals which arise from 

 the ectoderm (PI. lxii., fig. 1), and have a general radial direction; many of the 

 canals pass into the mesenteries. 



In Isaurus the canals are relatively much smaller than in Zoanthus, and are 

 more broken up than in Z. coppingeri, and undoubtedly have an endodermal as 

 well as an ectodermal origin (PL lxiii., figs. 5 and 6). 



The chief featm'e of the canal system in Parazoanthus is the presence of an 

 encircling sinus, which lies just beneath the endoderm, and extends throughout the 

 whole body- wall. This sinus is not everywhere continuous, but is frequently 

 crossed by bars of mesogloea (PI. lix.j fig. 8). It is connected with the ectoderm 

 by radial, occasionally branched canals. In P. anguicoma and P. dixoni, and in some 

 other species, very fine canals connect the sinus with the endoderm (PL lix., fig. 9). 

 Although the encircling sinus may have connexions with the endoderm, these are 

 very delicate, and the sinus itself is undoubtedly of ectodermal origin. The 

 encircling sinus is the same as the "ring-canal" described by Erdmann in his 

 " sp. 8 Palythoa sp." (1885, p. 469). [This is the Palythoa anguicoma of Hertwig, 

 which we believe to be another species, for which we would suggest the name 

 Parazoanthus hertwigi.'] Nematocysts are present in the canals of many of the 

 species of Zoanthus and Parazoanthus ; possibly they are of universal occurrence 

 in the canals. 



In Gemmaria macmurrichi a somewhat similar encircling sinus is present, but it 

 is very largely broken up by the mesogloea into a number of vertical canals which 

 appear in transverse section as a series of lacunae, each one lying immediately 

 below the union of a mesentery with the body-wall (PL lxiii., fig. 7). These 

 vertical canals are often connected by finer ones. 



Lacunse are found in all the genera of the Zoanthese except Epizoanthus and 

 Sphenopus. In Zoanthus it appears that the canals are more or less broken up to 

 form the lacunae, least so in Z. coppingeri and Z. dance (as identified by Hertwig), 

 and most so in Z. jukesii (PL lxii., fig. 2), in which species continuous canals are 

 rare ; the same also obtains in Isaurus asymmetricus. In Palythoa there are no 

 continuous canals ; but lacunas are present, as these are so similar to those which 

 we know to be of ectodermal origin in other species; and as nematocysts are 

 present, we believe that these lacunae are of ectodermal origin (PL lxiii., figs. 8 

 and 9). 



Small groups of cells, iiTegularly scattered in the mesogloea, are especially 

 characteristic of the genus Epizoanthus ; they may be very numerous, as in E.pagu- 

 riphihis (PL lix., fig. 6), and in some of the species described by Erdmann, but in 

 other species, E. i^icrustatiis, E. couchii, and E. wrightii, they are very rare. They 



