PKOCEEDmGS OP THE BRITISH ASSOCIATION. 
427 
propensities of Dermestes minimus. He believed that the paste was most fre¬ 
quently attacked by AcaridcB^ and the leaves of books by Coleopterous larva3. 
He had tried many means to defend his library, but the most successful was the 
securing the circulation of fresh air round the books, which could be done by 
removing them an inch or two from the wall, and a few lines from each other. 
The Rev. F. W. Hope stated, that in America paper had been dipped in an 
infusion of Quassia as a preservative against insects. 
Mr. Ball exhibited some living specimens of a new species of Heath named 
Erica Mackaiana. It most nearly approached E. tetralix^ from which it differed 
in the whorls of leaves of the flower-stalk being continued quite up to the pedicels 
of the flowers. In E. tetralix the whorls gradually disappear, and the flower stalk 
is quite naked for some distance below the pedicels of the flowers. The plant was 
found growing in the same districts with E. tetralix, and invariably retained the 
above character perfect. 
Professor Graham objected to admitting this plant as a species. He thought 
it nothing more than a variety of E. tetralix, and was very much opposed to the 
system of multiplying species. 
Mr. Lankester remarked that there was great difficulty in determining what 
constituted a species and what merely a variety. Unless some rule could be laid 
down, by which the value of the characters of a species or variety could be deter¬ 
mined, the arranging a new and constant form of a plant under either head must 
be left to the taste and judgment of the discoverer. 
Professor Henslow thought that if the seeds of new forms of plants could be 
collected and grown in botanic gardens, the value of their characters might be 
determined by the constancy of their reproduction. 
After some further remarks on the subject, from Messrs. Babington, Ball, and 
Mackay, the section concluded its meeting for that morning. 
On Tuesday the section was better attended than on the former morning. The 
President commenced the business of the morning by stating that he was about 
to read a letter which, although not from a professed naturalist, would throw 
some light on a question at issue between two eminent comparative anatomists* 
He alluded to the difference of opinion on the development of Crustacea that 
existed between Mr. Thompson and Professor Rathke of Berlin. The former 
denies that Crustacea pass through any changes previous to their assuming their 
perfect form, whilst the latter contends they do undergo certain changes. It 
might appear at first sight, strange, that animals so high in the scale of organisa¬ 
tion as Crabs and Lobsters should undergo the same changes as insects; but he 
thought the facts contained in the letter would settle the subject. It was 
extraordinary that Mr. Thompson should take the view he did, as he had long 
