*JoimL;STiS'] NEW BOOKS, WITH SHORT NOTICES. 311 
Athecata, Hydroids witli a polypary, but without calycles ; and 
Thecapliora, those with true calycles. There follows under each of 
these heads an analytical key on the binary plan, by which the 
genera are indicated. The species are then described at length, as 
well as the genera in the more taxological portion of the work. 
The author's notions on the j^rinciples of general philosophical 
classification are very forcibly expressed, and will be seriously 
questioned by many thoughtful naturalists. We admit that he 
has strong arguments in favour of uniting all the naked-eyed 
Medusae to the Hydroida. But then there is the important fact of 
the independent development of Lizzia (a species which directly 
reproduces itself), which cannot be overlooked. The author's 
reversion to the use of the terms Siphonophora and Discophora 
seems to us to be objectionable, if from nothing else, because these 
terms are less significant of morphological characters than the terms 
Calycophoridse and Physophoridse of Huxley. We fancy that 
Mr. Hincks, in trying to classify these organisms for the conve- 
nience of the student, has in some cases sacrificed a natural for a 
more arbitrary method. But of course this is a question on which 
opinions must and will differ. 
The accounts of the genera and species, the synonymy, habitats, 
bibliography, and general natural history are all excellent. The 
plates are sixty-seven in number, and though in some cases a little 
flat and wanting in artistic beauty (owing, we believe, to having 
been printed from " transfers "), they are, on the whole, admirable 
representations, faithful and well arranged. With a good micro- 
scope and this volume, the naturalist who can spend a month at 
the sea-side is greatly to be envied. 
Facts and Arguments for Darwin. By Fritz Miiller. With Additions by 
the Author. Translated from the German by W. S. Dallas, F.L.S. 
London: Murray, 1869. — Those who still find a difficulty in 
recognizing the force and importance of the law of " natural selec- 
tion " should read this work of Miiller' s with care. It certainly is 
one of the most powerful appeals to the inflexible logic of facts 
that has been made, with the exception of Darwin's own reasonings. 
The author, with the help of a multitude of excellent woodcuts, 
goes into the whole question of the morphology and development 
of the Crustacea. He thus lays before his readers a host of facts of 
the most complex character. He attempts to explain and unravel 
these by means of the old teleological idea, and fails. He then 
applies the Darwinian doctrine, and shows that it affords — within 
limits— a satisfactory solution. Certainly his explanation of the 
relation of the adult Tanais Dulongii to the Zoeae forms is most 
remarkable and significant. Mr. Dallas has given us a very read- 
able translation, and has done good service to science by intro- 
ducing MuUer's work to English readers. 
Remarques siir le Developpement d'une Planariee Dendrocoele, le Polycelis 
Icevigatus. Par Leon Vaillant. Montpellier : Boehm et Fils, 1868. 
— This memoir, which is now published separately, originally 
appeared in the Proceedings of the Academy of Sciences of Mont- 
