268 
serves as a standard to which all the other members of 
the group may be referred. The method is familiar 
enough, but has fallen into discredit because previous 
authors have made too little use of 1t and have confined 
themselves to the description of one or two animals as 
examples of a large class, whence it has resulted that 
students have too frequently formed narrow conceptions 
of animal structure and have underestimated the wide 
range of variation of which animals belonging to the 
same class are capable. The “Traité de Zoologie 
Concréte” has the merit of having avoided this error by 
describing a morphological type, not only for each class 
or subclass, but also for each order, suborder, and even 
for each tribe. Thus a general description is given of 
the morphological type of the order Octanthida (Alcy- 
onaria) ; Kophobelemnon is taken as a type of the sub- 
order Pennatulidz ; Renilla, Umbellula, Kophobelemnon, 
Pennatula and Gceendul are taken as the morphological 
types of the five tribes into which the Pennatulidz are 
divided, and a sufficient description of the families and 
genera included in the tribe follows the description of 
each type. This system is consistently adopted through- 
out the work, and as the types are illustrated by well- 
designed schematic drawings, the essential characters of 
all the subgroups are brought in the clearest possible 
manner before the mind. 
The book gives evidence of a minute acquaintance 
with zoological literature, and the numerous illustrations 
are largely copied from treatises of ‘a recent date. In 
the latter respect, the volume on the Ccelenterata is 
considerably in advance of other text-books, for it is only 
too frequently the case that old and sometimes obsolete 
illustrations are copied from book to book, while more 
recent work is ignored. 
The classification adopted does not depart widely from 
accepted lines. The Coelenterata are divided into two 
branches, Cnidarea and Ctenarea, the latter being co- 
extensive with the Ctenophora. Though some authors 
would separate the Ctenophora from the Coelenterata on 
the ground that they have an embryonic mesoblast, 
MM. Delage and Hérouard give sufficient reasons for 
retaining them in the phylum in which they have so long 
been classed. 
The Cnidarea are divided into two classes, Hydro- 
zoaria and Scyphozoaria, the former including all the 
forms usually classed under Hydrozoa, except the 
Scyphozoa, which have been placed along with the 
Anthozoa in the class Scyphozoaria. The union of 
these two groups is a step in advance, abundantly justi- 
fied by recent anatomical and embryological researches. 
In the class Hydrozoa it is noticeable that the Siphono- 
phora are raised to the rank of a subclass, the other 
subclass, Hydrophora, including the Hydride, the Hydro- 
medusze, the Trachymedusz and Narcomeduse. The 
grounds for this distinction are probably sufficient, but it 
is open to question whether the classification of the 
Siphonophora adopted in this work is an improvement 
on that of Heckel, and one cannot but regret that the 
authors’ love of symmetry or their anxiety to satisfy the 
claims of priority should have led them to abandon well- 
known and generally accepted names for others which 
are unfamiliar. For example, the order Chondrophorida 
sounds strange to most ears; the name is due to 
NO. 1707, VOL. 66] 
i NATURE 
[JuLY 17, 1902 
Chamisso, but has never come into general use, and 
that of Disconecté is preferable because better known. 
Again, in the Scyphozoaria the name Octanthide, derived 
from the Octactinia of Ehrenberg, is preferred to Alcy- 
onaria, though the latter is in general use and there is 
no good reason for abandoning it. The name Actin- 
anthidz, again, is substituted for Zoantharia, without 
sufficient reason, and the classification of the order is 
open to many objections. It scarcely seems consistent 
to class Edwardsia and Tealia under the Hexactinide, 
though the authors justify the inclusion of the former 
genus because of Faurot’s discovery of micromesenteries 
completing the first cycle of six pairs in certain species. 
The division of madreporarian corals into Hexacorallidze 
and Tetracorallide is quite unjustifiable in the present 
state of our knowledge, and in spite of their sharp criti- 
cism of Miss Ogilvie’s work on the microscopic characters 
of the corallum (p. 602), the authors might have given her 
the credit of having demonstrated the unity of structure 
in recent and so-called rugose or tetracorallid corals. 
Indeed, they are open to the charge of inconsistency in 
this respect, for they have borrowed largely from her 
figures and adopted her possibly erroneous views on the 
mode of formation of the corallum, but have refused to 
accept some of her most important and well-grounded 
conclusions. It is scarcely possible, at the present time, 
to retain the groups Aporina and Porina (Aporosa and 
Perforata of Milne-Edwards), though it must be con- 
fessed that no acceptable alternative has been offered, 
and MM. Delage and Hérouard, while retaining a dis- 
credited classification, give a very good summary of the 
various schemes that have been proposed by different 
authors. ; 
Knowing the previous writings of M. Delage, one is 
not surprised to find that, in discussing the origin of 
atolls and barrier-reefs, he takes the opportunity of 
making a double attack on the Darwinian theories of the 
formation of coral reefs and natural selection. It is tobe 
regretted that he allows himself to write so dogmatically 
on these subjects, for it is by no means the case that the 
theory of natural selection has been abandoned by 
zoologists in general as a “hypothése séduisante,” attrac- 
tive but inadmissible. He would seem to have over- 
looked the school of statistical zoologists, whose work, so 
far as it has gone, has done much to strengthen the 
opinion that natural selection is by far the most potent 
factor in the evolution of species. Finally, when the 
complete results of the boring at Funafuti are published, 
M. Delage will probably be obliged to admit that the 
great English naturalist was not far wrong also in his 
speculations on the origin of atolls and barrier reefs. 
G. C. BOURNE. 
WAVES AND SOUND. 
Wellenlehre und Schall. Von W. C. L. van Schaik. 
Translated into German by Dr. Hugo Fenkner. Pp. 
xi+358. (Brunswick: F, Vieweg and Sohn, 1902.) 
Price Mk. 8. 
O portion of physics is more difficult to treat in an 
elementary way than that of sound ; the conse- 
quence is that though advanced treatises of magnificent 
quality exist, an elementary text-book in English which 
