88 
REVIEWS, 
nera contained in the second and third volumes ; of which the execution, 
generally speaking, is inferior to the first. In this, we find particulars to 
be corrected and supplied; in the others, a complete remodelling would be 
often requisite. In not a few instances, we should be at a loss to deter¬ 
mine the genera from the characters without the help of the figures; it is 
the more to be regretted that the style of the plates in the last two volumes 
is strikingly inferior to those given in the first. There are portions which 
we may except from this criticism, as the sub-families Borborides and Hydro - 
myzides ; the last volume, also, is much superior, on the whole, to the 
second. 
The next thing essential in the composition of a work of Natural His¬ 
tory is accuracy in the determination of the species, and the application 
of the trivial names. Considering the nature of the subject Mr. Walker 
had to treat, a mistake here and there does not seriously detract from the 
merit of the work. We doubt if any one can have gone beyond a very 
superficial study of the Diptera without discovering how difficult it is to 
determine the species with certainty, not only from the brevity of the de¬ 
scriptions given by nearly all the older authors, but also because of the 
hasty and undigested publications of writers who, instead of making the 
interests of science their end, have treated Natural History as the means 
of gratifying a puerile vanity. We, at least, are thoroughly persuaded of 
this, and are, therefore, not disposed to quarrel with Mr. Walker’s book, 
because we cannot always agree with him as to the identity of species, 
such as, for example, Leptis scolopacea , L. strigosa , Bombylius ctenopte- 
rus , Chrysotoxum intermedium, Eumerus selene, Asilus cristatus, A.fim- 
briatus, Empis unicolor, &c. But, in some other instances, it appears as 
if Mr. Walker could scarcely have gone astray, as he has done, if he had 
studied the works of previous writers with a little more attention. It has 
probably been owing to the limited materials at his disposal that he has 
united together species indubitably distinct, as is the case under Hcemct- 
topota pluvialis, Bombylius major, B. medius, Syrphus pyrastri, S. scala- 
ris, Tetanocera cucularia, Myopa ferruginea, M. atra, Trypeta heraclei, T. 
artemisice, T. serratulce , T. arctii, T. solstitialis, and many more that we 
could name. In other places, mere varieties are treated as species; at 
least, the characters he gives are insufficient to convince us of the value of 
such species as Sargus nubecidosus, Chrysomyia flavicornis, C. cyaneiventris, 
Stratiomys subvittata, Criorrhina ranunculi, Microdon apiformis, fyc. Such 
occasional mistakes, however, are of much less consequence than the confu¬ 
sion which affects some genera and families throughout, in this respect, 
