D.—ZOOLOGY 67 
the groups as indicating elements composing the fauna and flora which 
had arrived at different times. Further, by comparing the European 
distribution of the British species, he suggested the directions from which 
those different elements had arrived and the relative times of their 
arrival. He recognised three preglacial groups, the ‘ Lusitanian’ in the 
west of Ireland, which he believed came from the Spanish peninsula, the 
“Gallican,’ in south-east Ireland and south-west England, from the 
Mediterranean region, the ‘ Kentish,’ from the same source, but later, 
the ‘ Scandinavian,’ which came with the Ice-age from Northern Europe 
and occupies north-west Scotland and northern and western Wales, and 
the ‘Germanic’ element, the great post-glacial invasion occupying a 
large part of Ireland, southern and eastern Scotland and north, middle 
and east England. Forbes regarded each succeeding invasion as having 
driven the earlier inhabitants from the territories previously occupied by 
them, the whole theory being based upon the struggle for existence, 
species better adapted to the changed conditions pushing out the less 
well adapted. But, as in the case of the communities in their habitats, 
is this the whole story? Experiment shows that at least some species 
can be reared in districts far beyond their normal range. ‘Two of the 
southern and south-eastern species lived in my tubs in north-east Ire- 
land and I had succeeding generations each year. One of Forbes’s 
Scandinavian species, with a British distribution limited to northern 
and western Scotland and north-west Ireland, lived and bred freely in 
_ my tubs in north-west Ireland and later in Cambridge. Someone will 
say ‘ Yes, but these beetles were protected in the tubs.’ Protected from 
what? I imagine that they were chiefly protected from moving else- 
where, from exercising choice. If the struggle for existence were the 
whole explanation of the grouping, how can we account for the fact that 
some species in our islands do not occur under similar conditions to those 
under which they are found on the Continent ? To take, for example, 
one of the north European species * which should belong to Forbes’s 
Scandinavian type; until the last few years it has only been found in 
south-east England and East Anglia, except for a record for a single 
specimen taken in the Isle of Man in 1gro,!* but in 1930 it was found in 
Durham," and in 1933 in Forfarshire in a place which was thoroughly 
worked in 1908 and where the beetle certainly did not occur.!® Another 
Scandinavian species, common in many of the Scottish lochs, flourishes 
in a lake in Berkshire, and certain other ‘ northern’ species occur in the 
New Forest and in Devonshire, apparently perfectly adapted to the very 
different climatic and organic conditions. Thus it is not only internecine 
strife or lack of adaptability which has caused the changes in the fauna 
but also movements of the insects stimulated by choice, an attribute of 
13 [lybius subeneus, Er. 
14 F. Balfour-Browne, ‘The Aquatic Coleoptera of the Isle of Man, etc.’ 
Naturalist, 1911. 
18 Joyce Omer Cooper, ‘ Some Notes on Dytiscide collected in Northumberland 
and Durham in 1930,’ The Vasculum, vol. xvii, 1931. 
16 F. Balfour-Browne, ‘ The Aquatic Coleoptera of the County of Angus, etc.’ 
Scottish Naturalist, 1934. 
