REVIEWS. 
69 
right to require in a work of this nature. These are partly indispensable to 
every scientific work on Natural History, partly requisites attaching to the 
special character of a Fauna. Under the former head, we may reasonably 
expect that the classification should not fall behind the actual progress of 
the science. It may justly be said, in praise of Mr. Walker’s book, that 
here it need not fear comparison, but that as to the systematic arrangement 
it excels the Diptera of Sweden by Zetterstedt, admirable as this is in other 
respects, and that in some points it even constitutes a step in advance, and 
not an inconsiderable one. 
The extent which Mr. Walker assigns to the order Diptera corresponds 
with the ideas of a certain school of Entomologists better than with the in¬ 
dications of nature. The combination of the Suctoridea (Pulex X.) with 
this order will scarcely stand the test of a close examination of their ana¬ 
tomy, internal and external. The remainder of the order, after the removal 
of these, is divided into Proboscidea and Eproboscidea ; the names are open 
to criticism—not so the principle of the division itself. The Proboscidea 
Mr. Walker subdivides into Nemocera , Brachycera , and Hypocera . But 
while he has seized correctly the characters which distinguish the Hypocera 
from all the other families of Brachycera , it seems to us that it would have 
been better to have treated them as a subordinate division of these, than to 
make of them a co-ordinate group—a rank not justified either by the number 
of species, or the variety of forms which they comprize, nor yet by the im¬ 
portance of the distinctive marks which separate them from the rest of 
the Brachycera . 
The first two volumes contain the Brachycera divided into nineteen fa¬ 
milies: the number alone plainly shows that it has been the author’s 
purpose to avoid an excessive multiplication of the families; a laudable 
endeavour, considered in reference to the specific object of the work. The 
classification does not evince as much care to fix the bounds of the families 
with some regard to a fair proportion between their respective contents. 
No doubt, nature has set limits to such an attempt, and they cannot be 
overstepped; but Mr. Walker might have made a closer approach to these 
natural limits, if he had reunited some of the smaller families, and had sub¬ 
divided his immense family Muscidce in a suitable manner. The last it 
was in his power to have accomplished, and we cannot but regret that he 
has declined the undertaking. The other is a task so difficult that we have 
no right to exact it, however thankful we should have felt to him for a 
successful solution of the problem. 
The analytical table of the families is skilfully constructed, though it 
