A PRELIMINARY LIST OF THE INSECT-FAUNA OF MIDDLESEX. 207 
All the above statements and suggestions are purposely of a 
very general character, because it is hoped that further informa- 
tion on many points will be available before any analysis of the 
details need be attempted. Sooner or later, it will be desirable 
to make a searching comparison between the fauna of the several 
localities and the present and past fauna of each locality, where 
they can both be ascertained. Where we know species to be non- 
existent in Middlesex, but abundant in Surrey or some other 
neighbouring county (e.g., various chalk species), an analysis of 
the records of wandering specimens may help us to estimate the 
extent to which some insects stray from their natural habitats. 
If we can ascertain how many exotic insects are imported into 
London by various means, and of these how many succeed in 
establishing themselves, it may throw light on the changes pro- 
duced in faune by immigration. It will, doubtless, be found that, 
if the circumstances are favourable, the introduction of a very few 
individuals is sufficient to start a thriving colony, but that many 
species may be introduced in numbers and yet never gain a footing. 
Thus it might possibly be shown that the non-existence of certain 
common continental species in England was not simply due to the 
intervening channel.* One of the most striking features of the 
list is the absence of several species which are generally looked 
upon as common. It will be interesting to see whether they are 
really wanting or merely not observed (so many lists have been 
received that, in the latter case, they must be rare), and to 
ascertain the reasons for their non-appearance. 
May I venture to suggest that Middlesex entomologists, 
especially those who have resided long in the county, should 
summarize their experiences as relating to the above-mentioned 
points, and send their notes to the Editor? Such notes might 
be gathered together and published from time to time under the 
heading, ‘‘ Insect-Fauna of Middlesex,’ and would surely contain 
much of value that would otherwise be lost, or, if published, 
rendered more or less inaccessible by being scattered through 
various journals and various years. 
(To be continued.) 
* The molluse Clausilia biplicata illustrates this. It is common on the 
continent, and yet almost extinct in England, occurring very locally near 
London. In fifty years it will probably be exterminated. Yet there is good 
evidence to show that it is an indigenous species, now dying out, and not a 
mere importation. 
