56 
THE VOYAGE OF H.M.S. CHALLENGER. 
be totally absent. There is a possibility that they may have been removed or overlooked. 
At all events further and more precise observations are necessary before their entiin 
absence can be held to be proved. The possibility of scales being present in Palmyra 
gives a different aspect to Eisso’s ^ description of Eumolphe fi'agilis, a species he found 
under stones on the shores of the Mediterranean ; and the same may be said of Claparede’s 
genus Pontogenia^ from Naples. 
Family Polynoida:. 
This family is represented in the Challenger collection by a very large number of 
species, and a few of these by many examples. Thus while in the important work of 
Kinberg on those procured during the voyage of the Swedish frigate ‘‘ Eugenie,” thirty, 
including the Iphionidse, are described, and Grube’s Philippine forms collected by Semper 
amount to eighteen, those of the Challenger reach to about fifty. 
In discriminating the species, little reliance (and in this De Quatrefages agrees) has 
been placed on the number either of the segments or on that of the scales, within 
certain limits. The position of the antennae and tentacles and the general structure of 
the head in many cases is more satisfactory. Moreover, though Claparede thought that 
it was wrong to place too great weight on the bifid or simjffe condition of the bristles, 
there cannot be a doubt that the minute structure of both dorsal and ventral bristles is 
absolutely essential in any efficient diagnosis. Some authors, such as Grul)e, give a 
drawing of a scale and no other part of a species, but it is well to remember that in 
many cases scales are absent, and that it has never been proved that the characters 
afforded by the bristles are unreliable. Bristles alone, it is true, do not suffice to 
establish genera, but it is worthy of note that they carry with them important corre- 
sponding characters, in other parts. To say that the bristles of the same foot are bifid and 
simple, and hence belong to different genera, conveys little information. There are many 
different kinds of bifid bristles, just as there are many varieties of sim|)le bristles. It is 
only by a careful study of external configuration, head, scales, bristles, and other parts, 
that forms so closely allied, yet so distinctly (if delicately) separated, can be thoroughly 
elucidated. It is often a laborious, and sometimes a hopeless task to discriminate closely 
allied forms by description alone. A siagle accurate figure would put the question at 
rest. Thus it is very difficult to come to definite conclusions with regard to most of the 
Annelids described by Grube in his Annulata CErstediana, and so with many given by 
De Quatrefages ; and the expenditure of time is often greater in such cases than is 
warrantable, for the authors had not closely allied forms in view when making their 
brief and often superficial descriptions. It is surprising to find such recent and excellent 
^ Hist. Nat., Ac., iv. (1826) p. 415. 
Op. cit, p. 57. 
