34 Proceedings of the Royal Physical Society. 
For the plants, a beginning has been made in the Zypes of British 
Vegetation and other papers of British plant ecologists. As to the fauna, 
the strength of the argument should, I think, appeal to any true field 
naturalist who has a fair acquaintance with entomology. The published 
lists of distribution, moreover, clearly indicate the wide opening in this 
kind of investigation. 
We cannot give here detailed examples of plant and animal association, 
because none has yet been worked out with sufficient thoroughness. As an 
example of a study of the distribution of British freshwater mollusca on 
modern ecological lines, a paper “On the Geographical Distribution of 
Mollusca in South Lonsdale” may be noted (7). In America the study 
of animal ecology is being prosecuted with vigour, and a number of papers 
have already been published (8). 
Numerous insects, arachnids, crustaceans, worms and protozoans are 
aquatic in some or all of their life stages. All these, of course, are limited 
to the neighbourhood of various aquatic formations, and while the larger 
forms and predatory species are often powerful migrants by land, air, or 
water, others are unable to stem the slowest stream, or bear for the shortest 
periods any but the moistest atmosphere. A wide range of distribution is 
therefore to be expected amongst aquatic species, and especially those of 
amphibious habits. As in the case of all animal associations, the most highly 
organised forms usually acquire the widest range of habitat, and may form a 
component in several different associations of the lower forms of life. The 
various species of waders, ducks, gulls, auks and divers affect very different 
stations during their summer residence, and in this they appear to be equally 
guided by their nesting habits and their food supplies. Their presence 
reacts powerfully upon the vegetation of their stations and on the other 
faunas. Even so restless a creature as the Dipper is almost confined to 
certain reaches of the stream-belt, the Kingfisher to others, while the Otter 
may be met with from mountain tarn to river mouth and sea-worn cave. 
Many insects, like the /epidoptera, are limited by the distribution of a 
food plant, but that this is by no means the only factor involved is shown 
by a comparison of the distribution of the various insects and their food 
plants. The lepidoptera of our sheltered woods, when compared with those 
of exposed situations like the moorland, differ as much in habits as in 
protective adaptations, and all have adopted food plants peculiarly prevalent 
in their associations. There is little doubt that all the principal plant 
formations have peculiar species of insects to be unravelled by the ecologist. 
As random and isolated instances, the “wainscotes” of our reed-belt and 
coastal formations, the “crimson underwings” of our oak forest, and the 
