682 
Analyses of Books . 
[November, 
removed to the front of the head. The alimentary canal probably 
extended to the end of the tail, and the present anus in the Ver- 
tebrates is therefore not the original one, but is a formation not 
inherited from any older group, but acquired within the group of 
Chordata. This transference of the anus is not easily accounted 
for on the Darwinian theory. 
At the end of this chapter we have a tabular scheme of the 
phylogeny of the Chordata. We find a series of hypothetical 
groups — the Protochordata, from which are supposed to spring 
the degenerate existing groups of Urochorda and Cephalocorda, 
and the hypothetical Proto-vertebrata. From these are descended 
a degenerate type, the Cyclostomata, and another hypothetical 
group, the Proto-gnathostomata. These give rise to the adtual 
Elasmobranchii and Holocephali, and the hypothetical Proto- 
ganoids, from which spring the existing Dipnoi, Ganoids, and 
Teleostei, and the hypothetical type Proto-pentadadfyloids. 
These are the ancestors of the real amphibians, and of a final 
hypothetical group, the Proto-amniota, the progenitors of the 
Sauropsida (birds and reptiles), and of the mammals. It is con- 
sidered probable that the mesozoic Plesiosauri and Ichthyosauri 
were more closely connected with the Proto-pentadadfyloids than 
either to the Amphibia or the Prota-amniota. 
The thirteenth chapter is devoted to an examination of the 
origin and homologies of the germinal layers, and to the consi- 
deration of the nature, origin, and affinities of larval forms. 
Here, from the difficulty of the subjedf, and often from the ab- 
sence of the necessary researches, the author aims more at 
summarising and criticising the views of others than at coming 
to any final decision. He considers that the gastrula reproduces, 
more or less closely, a stage in the development of the Metazoa 
which is permanent in the simpler Hydrozoa when the organism 
possesses a fully developed digestive cavity lined by the hypo- 
blast and endowed with assimilative powers. An oral aperture 
and an epiblast were in existence. The following weighty ques- 
tions, however, remain, as the author admits, unsolved : — “ By 
what steps did the compound Protozoon become differentiated 
into a Metazoon ? Are there any grounds for thinking that 
there is more than one line along w’hich the Metazoa have be- 
come independently evolved from the Protozoa ? And to what 
extent is there throughout the Metazoa a perfedt homology be- 
tween the two main germinal layers ?” 
The sedfion on larval forms begins with a comparison of larval 
and foetal development. Whilst examining this chapter we could 
not help regretting that so few embryologists are entomologists, 
or so few entomologists are embryologists. 
The remaining eleven chapters of the work, which want of 
space does not allow us to summarise, are devoted to organogeny. 
The author treats in succession of the epidermis and its deriva- 
tives ; of the nervous system ; the organs of vision, hearing, 
