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



between the pseudosepta, and were taken by Pourtales and others for septa of a second 

 order. 



The cyclo-systems have been described as circular in outline of summit, because this 

 may be regarded as their normal condition ; but very many of them are distorted in various 

 ways. One edge of the summit of the system is frequently elevated above the other, and 

 this elevation is on the side of the same face of the flabellum in all the calicles ; whilst 

 the dactylopores, on the opposite margin of the system, are frequently more or less 

 aborted. This condition forms a step towards that occurring in Cryptohelia, where all 

 the cyclo-systems have their mouths turned towards one face of the flabellum. The 

 cyclo-systems in the present species are also frequently elongated in a direction in the 

 plane of the flabellum, and in the case of those systems which are placed at the sides of 

 the main branches parallel with the line of extension of these branches. 



Besides being permeated completely by fine canals, the ccenenchym of the pore 

 systems is excavated by numerous rather large lacunar cavities, especially near the base 

 of the style and place of origin of an ampulla (PI. II. fig. 3). 



The ampullae appear, on both faces of the branchlets, as conspicuous rounded promi- 

 nences, set in groups, and often fused together into large papillated masses. They do not 

 occur on the flabellar faces of the main stem or branches. They present internally a 

 nearly spherical cavity, which communicates freely by openings with the canal systems 

 of the ccenenchym (PL II. fig. 3). 



Soft structures of Stylaster densicaulis (PI. VII.). 



Ccenosarc. — The outer surface of the coral generally, and of the cylindrical cyclo- 

 systems, is invested by a continuous surface layer of ccenosarc (PL VII.). This layer 

 dips down to line the dactylopores, and form the small tubulate sacs of the contained 

 zooids, and also is reflected into the wide cavity of the gastropore, the inner lining of 

 which is the greatly expanded sac of the gastrozooid, which zooid, deeply seated at the 

 bottom of the sac, occupies a very small area of its space (PL VII. A). Beneath the 

 surface layer the ccenosarcal meshwork forms a fine reticulation of smaller canals, and a 

 similar fine reticulation lies immediately beneath the lining membrane of the gastropore 

 (PL VII.). In the walls of the cyclo-systems, between these two finer reticulations, a 

 series of larger canals form an intermediately placed network, in which the branches 

 have a general direction parallel to the axis of the gastropore, and form a direct com- 

 munication between the basis of the dactylozooids and the large canals which spring from 

 the bases of the gastrozooids. Offsets of this reticulation pass up into the canals in the 

 interior of the pseudosepta. The three reticulations described are intimately connected 

 together by abundant anastomoses. In Plate VII. B B, the interior of a zooid cyclo-system 

 is represented with the sac of the gastropore and superficial lining network removed, in 



