382 Bibliographical Notices. 
BIBLIOGRAPHICAL NOTICES. 
A Treatise on Comparative Embryology. By Francis M. Batrour. 
Vol. Il. 8vo. London: Macmillan, 1881. 
In January last we noticed the publication of the first volume of 
Dr. Balfour’s ‘ Treatise on Comparative Embryology ;’ and the second 
volume, which has since made its appearance, affords a most bril- 
liant justification of the high terms in which we ventured to speak 
of this work. In the presence of such a book the ordinary critic, if 
he has any modesty in him, must perforce be dumb; and although 
we are quite prepared to hear that specialists may discover small 
errors or omissions inits pages, the excellence of the work is such that 
to dwell upon them would be an ungracious as well as an ungrateful 
proceeding. The author may certainly congratulate himself on 
having produced one of the grandest contributions to zoological 
literature that has appeared for years. 
The embryology of the Invertebrate groups having been treated 
of in the first volume, this second volume deals, in the first place, 
with the Vertebrates; but here we must note a peculiarity of classi- 
fication which may not meet with general approval. Dr. Balfour 
includes in the subject matter of this volume the embryology of the 
Ascidia; that is to say, he not only regards these animals as rela- 
tives of the Vertebrates, in accordance with the views of Kowa- 
leysky and others, but actually places them withthe Vertebrates, as 
forming part of the same highest group of animals, which he pro- 
poses to name Chordata. This great group is then divided into 
three subordinate ones—namely the Cephalochorda, including only 
Amphioxus, the Urochorda, consisting of the Ascidia, and the Ver- 
tebrata, or animals which show more or less distinctly a regular 
backbone. The members of the first two groups have probably, in 
the author’s opinion, undergone degeneration ; and the collocation of 
the three divisions seems to be borne out by their embryology. The 
Cephalochorda “undergo a less modified development than that of 
other Chordata.” 
The details of the development of the various great groups of the 
Chordata are worked out in the earlier chapters of the present 
volume with a care and patience deserving of all praise; and the 
whole subject is wound up by an excellent chapter giving a compa- 
rison of the formation of the germinal layers and of the early stages 
in the development of the Vertebrates. This is followed by another 
most interesting chapter on the ancestral form of the Chordata, which 
the author thinks must have belonged to a type allied to the Nemer- 
tine worms, which has now become totally extinct. According to 
his table of the phylogeny of the Chordata, both the Ascidians and 
Amphiowus lie out of the direct line of descent from these hypothe- 
tical ancestors of all Vertebrates. The final chapter of this section 
