60 THE VOYAGE OF H.M.S. CHALLENGER. 
between the pseudosepta, and were taken by Pourtalés 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. Il. fig. 3). 
The ampullz 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 coenenchym (PI. II. fig. 3). 
Soft structures of Stylaster densicaulis (Pl. VIL). 
Canosarc.—The outer surface of the coral generally, and of the cylindrical cyclo- 
systems, is invested by a continuous surface layer of cenosare (Pl. VIL). 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. VIL). 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 VIL. B B, the interior of a zooid cyclo-system 
is represented with the sac of the gastropore and superficial lining network removed, in 
