752 
THE VOYAGE OE H.M.S. CHALLENGER. 
“ Other Hy droid groups are at present under examination, and have already yielded 
some interesting results. 
“ The collection is very rich in the species of Cryptolaria, and the specimens it 
contains have furnished the means of working out in greater detail than had hitherto been 
done the structure of this curious group. Not only has the essential structure of its 
trophosome been thus determined and its stem proved to consist of two distinct elements 
— an axial, with which alone the hydrothecae are in connexion, and a peripheral, which 
forms an enveloping sheath for the axial — but we have been made acquainted with its 
Fig. 265 . — Monocaulus imperator, Allman ; one half the natural size. 
gonosome, which had not previously been detected, and which is present in a species 
dredged by the Challenger from a depth of 2600 fathoms. 
“ A new genus, Perisiphonia, has been constructed for the reception of some very 
remarkable species which agree with the Cryptolarim in the presence of an axial and of a 
peripheral system of tubes in the trophosome, but which differ from these in the very 
different form and relations of the hydrotliecse, while they are further characterised by 
the presence of a highly developed system of accessory receptacles analogous to the 
nematophores of the Plumularidse. 
“ The genus Grammaria is also well represented, and has been found to agree 
