2 
x 
NATURE 
[| NoveMBER 8, 1906 
histories and microchemical properties of the Proto- | 
zoa, Which may be said to have achieved their present 
culmination in the life and death of Schaudinn, 
worthily presented by Dr. Hartog. 
is 
Miss Sollas’s three chapters commence with a brief | 
historical introduction, followed by a lucid descrip- 
tion of two typical British sponges, Halichondria 
panicea and Ephydatia fluviatilis. The traces of a 
nervous system referred to on p. 39 of this volume | 
are not to be found here. Chapter viii. concludes 
with a key to British genera of sponges, comprising 
seventy-one names, and chapter ix. deals with ques- 
tions of reproduction, physiology, and the formation 
of flints. 
Turning now to Prof. Hickson’s valuable contribu- 
tion, we note that he treats the Coelenterata and the 
Ctenophora as separate phyla instead of regarding 
the former as divisible into two branches, the 
Cnidaria, those which are armed with stinging 
threads, and the Ctenophora, those which are pro- 
vided with swimming plates. A more serious change 
which he has introduced is the resolution of the old 
order Hydrocorallina into two distinct orders, Mille- 
porina and Stylasterina, the former second, the latter 
| phora. 
Prof. Hickson’s last chapter is concerned with 
those wonderful creatures of the plankton, the Cteno- 
In describing the planes of symmetry of the 
body, the author speaks of the tentacular or ‘ trans- 
verse’ plane and of the ‘‘ sagittal’’ plane. These 
animals show no antero-posterior differentiation, and 
only in one order, the Platyctenea, do they exhibit 
dorso-ventral differentiation; their symmetry is _bi- 
radial, and it is undeniably inaccurate to saddle them 
with transverse and sagittal planes. If a comparison 
with higher forms must be made, there are strong 
reasons for the belief that the tentacular plane of 
the Ctenophora should be likened to the sagittal 
plane of Bilateralia. 
In his account of the siphonophoran body (p. 298), 
Prof. Hickson evinces a general willingness to steer 
clear of wearisome polemical discussions; in this case 
the difficulty might have been surmounted by calling 
the various parts of the colony neither organs nor 
zooids, but organozooids. 
The volume concludes with six chapters on the 
Echinoderms from the pen of Prof. MacBride. In 
the classification of the Ophiuroidea the author has 
followed Prof. Jeffrey Bell’s system, which seems to 
Fic. 2.—Cucumaria crocea carrying its young. 
sixth, in the list of orders, separated in the text by 
the Gymnoblastea, the Calyptoblastea, and even the 
Graptolitoidea. 
With regard to the relations between the hydroid 
stock or hydrosome and the medusoid gonophore or 
medusome of the Hydrozoa, Prof. Hickson gives ex- 
pression to the perennial “‘ vexed question’’ as to 
whether the hydrosome preceded the medusome or 
vice versd; he does not assist the reader by adducing 
analogous instances. The stock and sexual stolon of 
some annelid worms would seem to offer an almost 
exact analogy to the hydroid and medusoid phases 
of a hydrozoan; the medusome might even be re- 
garded as an epitokous sexual phase, the stock being 
the parent form, indifferently whether it is fixed or 
free; the liberation of the medusz (where this occurs) 
would correspond broadly with the swarming of the 
epitokes. 
The general treatment of the three classes, Hydro- 
zoa, Scyphozoa, and Anthozoa, leaves little to be 
desired within the limits prescribed by the nature of 
the work, and prominence is given to bionomical 
questions. 
NO. 1932, VOL. 75 | 
XI. 
From ‘‘ The Cambridge Natural History,” vol. i. 
have achieved the distinction of permanency. The 
tabulation of the families of Asteroidea is based upon 
Prof. Perrier’s system, and gives a very different 
sequence from that based upon Mr. Sladen’s orders, 
also in vogue at the present time. In the chapter 
on the Echinoidea (sea-urchins) there are interesting 
passages on the physiology of the pedicellarie#; the 
chapter on the Holothuroidea (sea-cucumbers) con- 
tains a humorous though instructive comparison 
between the organisation of a Synaptid and that of 
a Sipunculid. 
The final chapter is devoted to questions of develop- 
ment and phylogeny. It seems probable to Prof. 
MacBride, and will doubtless appear so to his readers, 
““that Vertebrata and Echinodermata both arose from 
Protoccelomata.’’ It remains to be added that the 
illustrations are excellent, and many of them original. 
The term ‘ Statozoa,’’ originally applied to certain 
Echinodermata, but not generally adopted in that 
connection, may be conveniently extended so as to 
include such animals as sponges, ccelenterates, and 
echinoderms, in which a fixed condition is either 
actually or phyletically predominant. 
