380 Transactions. 



Fam. ANTHEAD^. 



HexactinicB with long marginal tentacles. Sphincter muscle slightly 

 developed or entirely absent. Numerous perfect mesenteries, and all (?) 

 furnished with reproductive organs. 



In the above I modify Hertwig's definition with respect to the sphincter 

 muscle, which I found to be absent in Actinia tenebrosa, and the non-ability 

 to cover the disc, which the same animal does completely and readily. There 

 still appears to be doubt as to whether all the mesenteries bear gonads. 

 McMurrich ("Albatross" Report) in describing Actinia infecunda says, " The 

 ova appeared to occur on a few of the larger perfect mesenteries." In 

 A. tenebrosa I found ova on what were apparently some of the mesenteries 

 of the second or third cycles. 



Genus Actixia (Browne). 

 " Antheadce with acrorhagi." 



3. Actinia tenebrosa (Farquhar). 



Pedal-disc. — Adherent. Rather wider than the column. The ectoderm 

 is thick, and secretes a thin cuticle. The nervous layer is fairly well de- 

 veloped. The mesogloea is thick, and in cross-section appears very fibrous. 

 The whole mesogloea of this animal is remarkable for the large number of 

 cells it contains, and is certainly the most highly developed mesogloea that 

 I found in the species I examined. The endoderm is thinner than the 

 mesogloea, and contains many gland-cells. 



Column. — The column is smooth. Its colour is brown, in shades varying 

 from reddish-brown to brownish-black. Mr. Farquhar records that he 

 found a specimen which was " yellowish-white, with a slightly greenish 

 tinge." He ascribes this colour to the absence of light. I have found these 

 yellowish-green specimens in such large numbers as to make me think that 

 they may possibly constitute a distinct variety of the species. 



The column forms a fairly well-developed collar under the bases of the 

 outer tentacles. On this are placed the marginal spherules, which are of 

 a whitish colour, with a blue or lavender tinge. 



The ectoderm of the column is similar to that of the pedal-disc. The 

 nerve-layer is more noticeable, and there are large nerve-cells. The mesogloea 

 is noticeably fibrous in appearance. 



Tentacles. — These are conical, and about half the diameter of the oral 

 disc in length. Their colour is dull red. They are placed in three cycles, 

 very crowded and numerous (200 or more). Their ectodermal muscles 

 are very strong, the processes of the mesogloea on which they are borne 

 being long and straight, lying side by side, parallel and not branching at all, 

 or only very slightly. There is a very thick nerve-layer between these and 

 the epithelial cells. The outer part is crowded with nematocysts, and there 

 is a thin cuticle. The mesogloea is about one-third as thick as the ectoderm, 

 while the endoderm is very thick, almost filling the cavity. The endodermal 

 musculature is only very slightly developed. 



Oral Disc. — The colour is the same as that of the tentacles. The mouth 

 is set on a prominent peristome. In structure the disc closely resembles 

 the tentacles, except that the mesogloeal processes which carry the ecto- 

 dermal muscles anastomose rather freely. The disc and tentacles can be 

 completely covered in contraction. 



