6 
THE VOYAGE OF H.M.S. CHALLENGER. 
cylindrical, but enlarging at its proximal end into a bulbous expansion which gives 
off from its base a dense plexus of capilliform tubes. 
Gonosome . — Gonophores ovate, borne in clusters on short, closely crowded, branching 
peduncles, which spring from a zone just above the base of the proximal circlet of 
tentacles. 
Localities . — Station 237, off Yokohama, Japan; lat. 34° 37' N., long. 140° 32' E.; 
depth, 1875 fathoms. 
Station 248, North Pacific; lat. 37° 41' N., long. 177° 4' W.; depth, 2900 fathoms. 
The magnificent species of Monocaulus to which the name of imperator has been here 
assigned was obtained in the North Pacific Ocean, from the enormous depths of 1875 and 
2900 fathoms. It far exceeds in size all known Hy droids. One of the specimens 
captured had its dimensions noted by Sir Wyville Thomson and Mr. Moseley imme- 
diately after being brought on board, and was found to measure 9 inches from tip to tip 
of the tentacles which form the proximal circlet, while its stem rose from its point of 
attachment to a height of 7 feet 4 inches. As Sir Wyville Thomson remarked, however, 
in a letter to myself describing the capture, the animal was measured as it lay extended 
over the surface of the trawl net, and though, of course, capable in life of becoming 
extended to the length then measured, this may not have represented the height 
habitually assumed by it. When in the state of extension which would seem to be 
normal to it the stem had a diameter of about half an inch. 
Immediately after the capture a drawing of one of the specimens was made by 
Mr. Wild, the artist of the expedition, and it is fortunate that this precaution had been 
taken, for though the specimens were at once put into spirits they have lost almost every 
character of importance. Indeed, Sir Wyville Thomson, writing to me from on board 
the Challenger soon after the capture of the great Hydroid, says “ these delicate things, 
drawn up rapidly through the water from a depth of nearly four statute miles, and 
transported into such totally different conditions of temperature, pressure, &c., suffer 
greatly from this violent change. They are, in fact, almost knocked to pieces, and their 
fine tissues are in a nearly deliquescent state, so that our great anxiety is to put them 
at once into some reagent which may tend to harden them. It is wretched to see them 
melting away absolutely under our eyes. When put into any of our fluids they at once 
contract out of all form. But this cannot be helped, and I thought it best that you 
should have them as well preserved as we could manage, so I only gave them a cursory 
glance and sent them on.” 
Notwithstanding the impossibility of preserving the animal in anything like a 
satisfactory state, some points by no means without interest have been made out in its 
structure. One of the most important of these is the fact that the stem, instead of 
having its axis occupied by a pith-like core as in Corymorpha, contains a wide cavity 
