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THE DEVELOPMENT OF THE 
INVERTEBRATES. 
Text-book of Embryology. Edited by W. Heape. 
Vol. i. Invertebrata. By Prof. E. W. Mac- 
Bride. Pp. xxxii+692. (London: Macmillan 
and Co., Ltd., 1914:) Price 25s. net. 
HE appearance of Balfour’s great work on 
comparative embryology in 1880 marked 
an epoch in the history of zoology. Since then not 
only has a vast quantity of new information been 
acquired, but whole new branches of the study 
have been developed. For instance, we now have 
the science of experimental embryology, which 
aims at discovering the conditions and regulative 
processes of differentiation and development 
science founded by Roux, Driesch, and others; 
while to E. B. Wilson and other American ob- 
servers we owe the study of-cell-lineage, whereby 
the prospect is opened up of being able to trace 
back homologous organs not merely to germ- 
layers, but to corresponding individual cells in 
the early history of the embryo. To give a clear 
and concise account of these modern researches is 
indeed a difficult task. Prof. MacBride is the 
first Englishman to make the attempt, and it may 
be said at once that he has been, on the whole, 
most successful. 
The descriptions are remarkably lucid, and easy 
to understand with the help of an abundance of 
really excellent illustrations. Each chapter deals 
with a separate group. After a brief introduction, 
it begins with as complete an account as possible 
of the whole development. of a typical example, 
from egg to larva, and from larva to adult. Other 
forms are then briefly compared with the type, 
and there follows a discussion of the general 
features of the embryology, of their phylogenetic 
significance, and of the affinities of the group. 
There is much to be said for this mode of treat- 
ment. The story of the development is continu- 
ous, and the reader is presented with a very com- 
plete picture of the ontogeny of a representative 
of each group. At the same time there is some 
danger that he may not fully realise how much 
diversity of development there often is among 
closely allied animals; and that the type chosen 
may be, and indeed often is, the most specialised. 
Following the history of normal development, we 
also find in many chapters an interesting discus- 
sion of the results of experimental embryology. 
Here and there the text is varied with useful notes 
on the occurrence and habits of larve, and on 
methods of collecting and preserving material. 
Such a work is bound to show weak points, and 
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the chapters are certainly of ,unequal merit. 
Readers will turn witl special interest to the part 
devoted to Echinoderms, since Prof. MacBride’s 
important researches on these animals are well 
known. They will not be disappointed, but will 
find, we think, the best account of the embryology 
of the Echinoderms yet published in any text- 
book. On the other hand, certain obscurer groups 
are altogether omitted, or are scarcely mentioned. 
Considerations of space may, no doubt, have com- 
pelled the author to aim rather at giving a full 
history of the more important forms than at com- 
pleteness. But we venture to think that it would 
have been better to devote more attention especi- 
ally to organogeny in the earlier chapters, and to 
have collected the parts dealing with experimental 
work into a separate volume. For the general 
questions, which the experiments are designed to 
elucidate, are far better discussed as a whole than 
piecemeal in the various chapters. Want of space 
has also prevented Prof. MacBride from giving 
any historical account of the subject, from refer- 
ring in most cases to any but the most recent 
publications, and from providing a fuller biblio- 
graphy. 
Knowing what difficulties the writer of a text- 
book has to contend with, it is an ungrateful 
task to find fault with so excellent a work. Yet 
some points may be mentioned which might well 
be improved in a second edition. We doubt 
whether the reader of the chapter on the Porifera 
would gather that there takes place in many 
sponges the remarkable developmental process 
known as the “inversion of the layers,” so well 
described by Delage, Minchin, and Maas. Since 
he admits, we believe quite rightly, that the 
Ectoprocta and Endoprocta are independent phyla 
“not descended from a common fixed Polyzoon 
ancestor,” why has not the author the courage to 
separate them, following the example of some of 
his predecessors? Again, we find the Opistho- 
goneata and the Progoneata still joined in the 
artificial group Myriapoda. Such conservatism 
cbscures the issue, and hinders progress. We 
wonder, also, why he retains the word nephridium, 
even in inverted commas, for the segmental ducts 
of Peripatus, derived from the ccelomic wall, and 
not homologous with the nephridia of the earth- 
worm to which Lankester first gave the name. 
Indeed, the whole question of the nephridia, their 
development and homology, seems to be very in- 
adequately treated. Here the author appears to be 
treading on unfamiliar ground, and to be insuffi- 
ciently acquainted with the literature on the sub- 
ject. Even less satisfactory is Prof. MacBride’s 
discussion of the coelom. Its origin is vaguely 
referred to the radial enteric chambers of some 
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