38 
THE VOYAGE OF H.M.S. CHALLENGER. 
from the axial tube and protrude externally through interstices between the tubes of the 
peripheral fascicle. 
The genus Cryptolaria was founded by Busk for a group of Calyptoblastic Hydroids, 
whose fascicled stems and sessile tubular hydrothecse, destitute of limiting floor, and 
adnate to the axial tube on its free portion, afford easily recognisable characters. 
The specimens obtained by the Challenger have furnished the means of working out 
in further detail the structure of this curious group, and not only of satisfactorily 
determining the essential constitution of its trophosome, but of rendering us to some 
extent acquainted with its gonosome, which had not previously been detected. 1 
The existence of two distinct elements, a peripheral and an axial, in the hydrocaulus 
of Cryptolaria is an important and unexpected character, and with the exception of four 
other genera, Lafoea, Lictorella, Perisiphonia, and Grammaria, for a knowledge of whose 
essential structure we are also indebted to the dredgings of the Challenger, Cryptolaria 
is the only genus, so far as is yet known, in which this condition is present. 
In all the known species of Cryptolaria the peripheral tubes cease to envelop the 
axial at some distance from the distal extremities of the branches, and the axial tube 
thus becoming free and naked shows here, without further preparation, the relation 
between it and the hydrothecse. The structure of that part of the colony where the 
axial tube is still covered by the peripheral can be best demonstrated by careful 
maceration in caustic potash, which diminishes the adhesion between the constituent 
tubes and facilitates their separation under the microscope. 
The gonosome has as yet been found only in three species of Cryptolaria. Two of 
these, Cryptolaria abyssicola and Cryptolaria diffusa, have been dredged from the 
vast depths of 2600 and 2500 fathoms respectively, while the third, Cryptolaria 
geniculata, has been brought up from a depth of 315 fathoms. In all these the relation 
of the gonangia to the axial tube is very similar to that of the hydrothecse, and like 
the hydrothecse, they protrude at intervals from between the component tubes of the 
peripheral fascicle. They suggest indeed an obvious comparison with the hydrothecse, 
from which they differ chiefly in their greater size and more sac-like form. No other 
element of the gonosome beyond the gonangia has been detected. 
The collection of the Challenger is very rich in the species of Cryptolaria. These 
have been obtained from widely separated localities and from various depths, ranging 
from 20 fathoms to nearly the greatest which have yielded any living forms to the 
dredge. No species of Cryptolaria have as yet been recorded from European seas. 
In distinguishing the species for purposes of systematic description the zoologist 
1 In the Report on the Hydroids of the Gulf Stream I described a remarkable structure which was found attached 
to the stems of a species of Cryptolaria, and which I regarded as exhibiting undoubted affinities with the Hydroid 
genus Coppinia, suggesting at the same time the possibility of its turning out to be the gonosome of the Cryptolaria, 
nothing having been at that time known of the gonosome of this genus. It is now evident that the structure in question 
is an independent growth, having nothing to do with the gonosome of the Hydroid on which it had taken up its abode. 
