74 
NATURE 
[Mov. 23, 1882 
than 36 species, and of these 33 are describe1 as new to 
science. Five other species found during the cruise of 
the Knight Errant are also included inthe report. These 
species are referred to 9 genera, of which three are 
described as new. ‘Those genera which range over 
the widest area, are also those which range most in 
depth—while there are some species peculiar to deep-sea 
areas. No truly generic types seem to be thus charac- 
terised. Dr. Hoeck considers that the Pycnogonide 
form a distinct and very natural group or class of Arthro- 
pods. Their common progenitor must have been a form 
with three jointed mandibles—multi-jointed palpi and 
ovigerous legs, with numerous rows of denticulate spines 
on the last joints. In the most primitive condition the 
eye of the Pycnogonid consists of a rounded transparent 
part of the integument, the inner surface of which is fur- 
nished with some small ganglia and nerve-fibres issuing 
from the integumentary nerve-bundle. The highly-deve- 
loped eye of the shallow-water species show ganglionic 
cells, distinct retinal rods, and a lens consisting of a 
thickened part of the chitinous skin of the animal. 
Those eyes which have lost their pigment and their 
retinal rods are rudimentary. Dr. Hoeck, treating of 
the affinities of this class writes: “about the relation in 
which the Pycnogonida stand to either the Crustacea or 
the Arachnida, we know as much or as little as we do 
about the relation in which these two classes of Arthro- 
poda stand to each other.” 
Vol. iv. opens with an important contribution to ana- 
tomical science in the Report on the Anatomy of the 
Petrels (Tubinares) collected during the voyage. It is 
from the pen of Mr. W. A. Forbes, Fellow of St. John’s, 
Cambridge. 
The group of Petrels is one that up to the present 
date can scarcely be said to have been anatomically in- 
vestigated. It is difficult at all times to procure speci- 
mens in the flesh—and some of the species are so large 
as to render their preservation a matter of considerable 
trouble. At the suggestion of the late A. H. Garrod, 
the naturalist staff of the Cha//enger made a fine collec- 
tion of these oceanic birds in spirits, which contained 74 
specimens belonging to 31 species and 22 genera. Prof. 
Garrod had scarcely commenced to work at this series 
before he was struck by the lingering illness which ended 
in his lamented and premature death, and his friend, Mr. 
W. A. Forbes, undertook to draw up the report which 
here appears. This report is of a very thorough charac- 
ter. Commencing with an account of the previous litera- 
ture on the anatomy and classification of the group; we 
then have a complete sketch of the comparative anatomy 
of the group--the external characters, pterylosis and 
visceral anatomy are first described—these are succeeded 
by an account of the myology—to which follows a descrip- 
tion of the tracheal structures and of certain other points 
in the anatomy of the soft parts, while an account of the 
osteology concludes the report. Some of the modifica- 
tions, described by the author, “are of great physiologi- 
cal and morphological interest, whilst the numerous 
differences in points of detail displayed in the different 
sections and genera of the Petrels, lead one to expect that 
the future study of systematic ornithology will be not a 
little elucidated by the labours of the anatomist wherever 
he has material, as in the present case, at his comm and, 
sufficient for an adequate study of a natural group on the 
basis of structural differences more important than those 
that can be discerned from the superficial inspection of 
an ordinary skin.” This report is illustrated by very 
numerous woodcuts and seven plates of anatomical de- 
tails. In treating of the affinities of the group, Mr. 
Forbes declares it to be a difficult task to assign to it any 
satisfactory position in any arrangement of the class of 
birds. 
The second report in the volume is on the Deep-sea 
Meduse, by Prof. Ernst Haeckel. They form one of the 
smallest and least important groups of the rich and re- 
markable deep-sea fauna discovered during the voyage of 
the Challenger. The number of species described does 
not exceed eighteen, of which half are Crasfedote and 
half Acraspede. These new species were briefly diagnosed 
in the “‘ System der Medusen, 1879,’’ but they are here de- 
scribed at great length and with a most splendid series of 
illustrations. The descriptive portion of the memoir is 
prefaced by a very elaborate sketch of the comparative 
morphology of the medusz, which is illustrated by many 
woodcuts. 
It would seem by no means certain that all the eighteen 
species of deep-sea medusz here described are constant 
inhabitants of the deep sea. The method of capture by 
the tow-net by which such delicate and fragile organisms 
are brought from great depths is still imperfect, and it 
seems probable that the greater number of medusze 
brought up apparently from the greater depths really 
swim in shallower water, and are only taken in during the 
“hauling-in” of the net. But Prof. Haeckel counts that 
those medusz which have either adapted themselves by 
special modifications of organisation to a deep-sea habit of 
life, or which give evidence by their primitive structure of 
a remote phylogenetic origin, may with great probability 
be regarded as permanent and characteristic inhabitants 
of the depths of the sea ; and as such he regards fourteen 
out of the eighteen described. With regard to the mag- 
nificent illustrations the author states: ‘‘It is of course 
impossible, from the imperfect state of preservation of 
the spirit specimens, to expect that they should be abso- 
lutely true to nature. I rather considered it my duty 
here, as in those figures in my ‘System der Medusen,’ 
which were drawn from spirit specimens, to take advantage 
of my knowledge of the forms of the living Medusz to 
reconstruct the most probable approximate image of the 
living forms, I was greatly assisted in my efforts in this 
direction by the skilful hand of my lithographer, Adolf 
Giltsch.’? It seems hardly necessary to make any scien- 
tific criticisms on this straightforward statement. 
The third and concluding memoir is by Hjalmar Théel, 
and contains the first part of his report on the Holo- 
thuroidea. It is altogether devoted to the holothuroids 
of the new order Elasipoda, which name has been with 
advantage substituted for that of Elasmopoda used in the 
Preliminary Report. Seven years have scarcely elapsed 
since the discovery in the Kara Sea of the form for which 
this family was established, and now over fifty species 
are known. These species of Elasipods are true deep 
water forms, and they may with all the more reason be 
said to characterise the abyssal fauna, as no single repre- 
sentative as far as is at present known has been found to 
exist at a depth less than 58 fathoms, Only one form, 
