16 
THE VOYAGE OE H.M.S. CHALLENGER. 
The mode in which the hydrophores form direct continuations of the segments of the 
stem is quite similar to the condition met with in Halecium dichotomum. 
The gonangia are for the most part borne in an entirely similar way on the free 
summits of the segments of the ramifications, thus taking the places which in other parts 
of the colony are occupied by the hydrophores. Gonangia are also occasionally borne on 
the summits of short lateral branches given off close to the free end of the segment. 
The gonangia present in the specimen appeared to be male, and their contents 
exhibited some curious and interesting features. Through the axis of the compressed 
pyriform gonangium the blastostyle (figs. 4 and 5, a) extends as a continuation of the 
coenosarc of the stem, and soon emits from its side a single gonophore (figs. 4 and 5, b) 
which continues to be surrounded by an ectodermal envelope (figs. 4 and 5, c ) from the 
sides of the blastostyle. The distal half of the cavity of the gonangium is occupied by 
a remarkable structure which lies like a cap over the summit of the gonophore, and 
consists of two concentric but laterally compressed hollow thick- walled hemispheres, the 
inner entirely embraced by the outer. The outer (fig. 4, e), which is in contact with the 
inner surface of the gonangium walls, is composed of radiating filaments, each of which 
under a sufficiently high power of the microscope may be resolved into a linear series of 
spherical corpuscles. The structure of the inner hemisphere ( d ) which lies in contact 
with the membranous envelope of the gonophore is more obscure, but would seem to 
consist of a plasmatic mass containing irregularly disposed nucleus-like corpuscles. The 
double cap which thus lies upon the summit of the gonophore in the young gonangium 
gradually atrophies as the gonophore advances towards maturity, and ultimately 
disappears (fig. 5) or leaves behind only a few radiating irregular threads as evidence of 
its former existence. 
Diplocyathus, n. gen. 
Name from SwrAoos, double, and KvaOos, a cup, in allusion to the accessory cup at the base of the 
hydrotheca. 
Generic Character. Trophosome. — Hydrocaulus a branching stem on which the hydro- 
thecse are replaced by hydrophores, each having a small cup of a different form at its base. 
Gonosome not known. 
This remarkable genus has strong affinities with .Halecium, from which it differs in 
the presence of a second cup-like receptacle at the base of every hydrophore. This 
receptacle is probably a true sarcotheca, and Diplocyathus would thus afford an additional 
instance of the presence of such bodies in Hydroids not belonging to the Plumularinse. 
It is impossible, however, to avoid a comparison of the accessory cup and its contents 
with the “ tentaculoid organs ” described by Hincks in Ophioides , 1 another genus having 
close affinities with Halecium. An examination of living specimens can alone afford 
1 Ann. and Mag. Nat. Hist., ser. 3, vol. xviii. p. 421, pi. xiv., 1886 ; British Hydroid Zoophytes, p. 230, pi. xiv. 
