THE VOYAGE OF H.M.S. CHALLENGER. 
viii 
this respect it is well to remember that many sj)ontaneously rupture on the slightest 
irritation. 
In regard to the preservation of the Annelids, it is unsafe to mix them with other 
classes, for when separation is carried out by hands that perhaps are imperfectly acquainted 
with the grou|), loose scales or cirri are apt to be overlooked, and are thus irretrievably 
lost. 
One important aid in dealing with any group was entirely absent, viz., coloration. 
The staff on board the Challenger w^as wholly inadequate to overtake this department, 
yet the beauty of the marine Annelids as a whole depends on the endless variety and 
often gorgeous loveliness of their hues. 
Methods followed in Description. 
In dealing with the materials placed at my disposal, an external survey of each 
was made under a lens, the structure of the feet, the minute anatomy of the bristles and 
hooks, as well as of the body-wall and other parts, was considered. It w'as impossible, 
however, to do more than glance at the anatomy of the group in passing, leaving for the 
present, for instance, such interesting questions as the nature of the remarkably folded 
organ (called liver by Johannes Steen at the anterior jiart of the alimentary canal 
(below and at the sides of the gullet) of Terehellides, for future consideration. Little 
reliance was placed on the description of the bristles and hooks without accurate representa- 
tions, since many species come so close that it would be very difficult for one’s successors 
to comprehend all the details. The distinctions while reliable are fine. Moreover, the hard 
parts just mentioned are less liable to be altered by the spirit than the soft tissues of the 
animals. The remarkable modifications observed in the bristles of every foot in many of 
the groups, and which are so disposed that a regular gradation in form exists between 
those at the superior border, and those at the inferior border, afford even a more complex 
subject for reflection than the changes undergone by the spines of an Echinoderm. 
Classification. 
The large number of new forms brought within our knowledge by the Challenger 
would have been supposed to lead to a noteworthy change in classification, but from the 
first it was apparent that no new family was required. All the types fell under the 
groups already constituted, and which have been very satisfactorily given by Malmgren 
in his Annulata Polychseta.^ A careful review of these groups in connection with the 
arrangement and relations of the nerve-cords, and the general structure of the body-wall, 
^ Jenaische Zeitsclir., Bd. xvi. p. 227, Jena, 1883. 
2 Helsingfors, 1867. 
