6 THE VOYAGE OF H.M.S. CHALLENGER. 
In one remarkable genus of Statoplea contained in the Challenger collection (Dip- 
locheilus (Pl. VIII. figs. 4-7), the hydrotheca presents a double margin formed by the 
development of an external chitinous sheath round the upper third of the hydrotheca, 
Nematophores.—The presence of nematophores, whether fixed or moveable, constitutes 
the most characteristic feature in the Plumularide. The nematophores are hollow 
chitinous bodies, more or less cup-shaped or tubular, and having their cavity in communi- 
eation with that of various parts either of the trophosome or of the gonosome, Their 
contents consist of protoplasm, in which thread-cells are often immersed, and which has 
the faculty of emitting pseudopodial prolongations which often attain great development, 
Those nematophores which belong to the fixed type are usually blunt spine-like bodies, 
with a continuous cavity and a terminal orifice, and with one or sometimes two lateral 
orifices. The terminal orifice is usually oblique or deeply emarginate. 
The nematophores of the moveable type are more constant in form. They are funnel- 
or trumpet-shaped, and never provided with lateral orifices. They are mostly bi-thalamic, 
their cavity being divided into a proximal narrow chamber and a distal wide cup- 
shaped chamber, separated from one another by a transverse perforated septum, The 
distal chamber opens by a wide terminal orifice, which is usually deeply emarginate on 
one side. 
Nematophores are either hydrocladial, hydrocauline, or gonosomal, according to the 
special part of the colony with which they are in immediate connection. An accurate 
knowledge of their arrangement and modifications will be best- acquired by examining 
them separately in the two great Plumularian sections. 
‘ Bodies resembling the nematophores of the Plumularidie have, however, been found in other Hydroids’ 
Hincks (loc. cit., p. 230, pls. i. iv. fig. 2) has constituted the genus Ophiodes for a remarkable Hydroid closely 
allied to Haleciwm, in which he had discovered certain singular bodies in the form of long cylindrical, very contractile 
tentacula-like appendages, each protected at its base by a small chitinous cup, through which it communicates with the 
coenosare of the colony, and terminating distally ina spherical capitulum, loaded with thread-cells. They occur here and 
there on the stem, at a slight distance below the hydrotheca, but are chiefly found scattered on the creeping stolon. 
Bodies closely resembling these have been found by G. O. Sars (Joc. cit., p. 109, pl. iv. figs. 5-8) in a Hydroid which 
he refers to the genus Ophiodes of Hincks, under the name of Ophiodes parasitica. This determination is not accepted by 
Hincks, who proposes for Sars’s Hydroid the new generic name of Ophionema, believing it to belong to the Plumularidie 
instead of regarding it with Sarsas a near ally of Halecium. Notwithstanding, however, the resemblance of Sars’s figures 
to a Plumularian, it is plain to me that the affinities of his Ophiodes parasitica are really with Haleciwm, and that the 
Norwegian zoologist had a true conception of its nature when he referred it to Hincks’s genus Ophiodes, The 
tentacula-like organs in Ophiodes would seem to take the place of the nematophores of the Eleutheroplean Plumularidze. 
They appear, however, to stand on a much higher grade of development than true nematophores, and to have passed 
out of the condition of mere protoplasm into that of a multi-cellular organ. If this be so we should not be justified 
in assigning to both the same significance. 
Belonging apparently to the same group of appendages are certain minute bodies which occur in Oplorhiza parvula, 
a little Hydroid allied to Lafoéa, obtained during the United States exploration of the Gulf Stream. They are here in 
the form of tubular receptacles, which are developed on the hydrorhizal network, and enclose a granular fleshy column, 
which supports a cluster of thread-cells (Hydroids of Gulf Stream, p. 14, pl. vii. figs. 1-8). In a nearly allied form, 
Lafocina tenuis, Sars, from the Norwegian seas, the hydrorhiza supports appendages which would seem to be essentially 
of the same kind (G. O. Sars, loc. cit., p. 119, pl. v. figs. 1-5). Minute fleshy processes of doubtful significance haye also 
