112 THE VOYAGE OF H.M.S. CHALLENGER. 



Numerous species of the genus Zoanthus have been described which resemble one 

 another closely, and probably only differ slightly in their anatomy, so that the species 

 can only be determined by the colour, the number and arrangement of the tentacles, &c. 

 This is the reason why I have not given any specific name to the single specimen of the 

 genus Zoanthus found among the Challenger material, in which the colour of the body 

 and the nature of the tentacles could not be made out, and why I have refrained from 

 giving any diagnosis of species, as from insufficient knowledge of the closely allied species 

 it is impossible to determine which characteristics belong to the whole genus and which 

 to the individual species. 



The colony, which was about 4 cm. long and 2 cm. broad, was firmly attached to a 

 stone, and consisted of some thirty individuals varying greatly in size. The smallest of 

 these are little knobs which hardly project 1 to 2 mm. above the ccenenchyma, the 

 largest are long cylindrical tubes, more than 1 cm. in length. They lie so thickly 

 compacted that the ccenenchyma is almost entirely covered, and only shows here and 

 there as a thin plate. The ccenenchyma is abundantly developed on the margin into 

 stolons, which are alternately broad and narrow. 



I made a thorough anatomical examination of three individual polyps of different 

 sizes, which were highly contracted like all the animals of the colony. The upper end of 

 the wall is not only contracted but inverted a little ; the only indication of the point at 

 which we can reach the interior of the body is a small navel-like depression. Apart 

 from the folds caused by contraction, the surface of the body is perfectly smooth. 



The wall (PI. XIV. fig. 4) is of considerable thickness, and consists histologically of a 

 homogeneous fundamental substance, with fine fibres embedded in it. The fibres are 

 hardly double contoured, are slightly waved, and run sometimes directly, sometimes 

 obliquely, from one epithelial surface to the other. They begin at the endoderm 

 with a granular enlargement which seems to pass directly into the epithelium ; towards 

 the ectoderm they branch repeatedly behind one another. They are furnished with 

 nuclei, and therefore bear a strong resemblance to the muscular fibres of the Ctenophora, 

 but their state of preservation did not admit of determining the histological value of the 

 fibres. 



The cells of the connective substance are strongly granulated bodies, either rounded 

 or branched. 



Finally, we find canals in the wall, such as do not exist in any other Actiniaria, 

 though they are found in the Alcyonaria. These canals vary greatly in diameter ; the 

 smaller are simple cords of cells, and only the larger ones show a lumen surrounded 

 by a layer of epithelium. As the canals repeatedly ramify and anastomose, they form a 

 thick net-work, which extends from the endoderm to the ectoderm, but is thickest near 

 the latter. Kolliker's observations show that in the Alcyonaria the canals are pro- 

 duced from the ectoderm, which is also the case in Zoanthus ; I have repeatedly found 



