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



apical and secondary branches, which on examination were seen to have secreted a 

 delicate horny sheath around the Gorgonid. The filamentous prolongations of the egg- 

 capsule of Dog-fishes and Skate may be sinnlarly invaded by the soft Gerardia, which 

 later extends over the various filaments and secretes a chitinous sheath around them. 

 These specimens, several of which are figured by Lacaze Duthiers, show clearly how a 

 transition may have taken place from the malacodermatous to the sclerobasic type. 



The polyps vary considerably in size, but are as well developed at the tips of the 

 branches as at the base. They may be 1 cm. in diameter at the base and may elongate 

 to 2 or 3 cm., while the tentacles reach a similar length in downwardly directed polyps. 

 On the other hand, the whole polyp may so far contract as to form a mammiform 

 tubercle on the sarcosome. The base of each polyp is irregularly polygonal. In 

 various places buds are present, which give rise to new polyps, — these are less frequent 

 on the main trunks, where the polyhedral character of the base is best seen. 



The tentacles are twenty-four in number, and are arranged in two alternate rows 

 of twelve each, the members of one row being slightly larger in hving specimens. The 

 mouth is oval and is surrounded by two thickened lips, which are an everted portion of 

 the stoniodamrn. The mesenteries, twenty-four in number, bear reproductive organs as 

 in the Actiniaria, and have at the free margin a thickened convoluted ridge occupying 

 one-quarter of its length. 



The ccenenchyma is unimportant in bulk, there being only a narrow strip between 

 adjoining polyps. It has, however, a structure which, so far as is known, is peculiar 

 to the family. It is traversed by a series of canals communicating with the polyps 

 at the base of each antimere, and by this means bringing all the blastozooids of a 

 colony into intimate communication with one another. OirripaAhes, amongst the Anti- 

 pathidae, appears to approach this genus most closely in the structure of its ccenenchyma. 

 The colour of the soft parts is greenish yellow, but near the reproductive season the 

 polyps become brick-red. 



The spicules, &c, sometimes contained in the ccenenchyma are those of Pennatuhda?, 

 Corals, Gorgonida?, Sponges, Foraminifera, &c, all of which become agglutinated to the 

 viscous ectoderm, but none are pecubar to it. 



The Homologies of the Mesenteries. 



In the foregoing account of the general structure of the zooids of the various genera 

 of Antipatharia I have purposely avoided any reference to a possible arrangement of the 

 mesenteries in pairs, and the term " interseptal " has been applied to the space between 

 any two mesenteries, and not in its technical and restricted sense as appbed to Zoantharia 

 generally. I have followed this course because the usual paired arrangement is not 

 marked in any of the species examined, unless it be in the mesenteries situated at each 



