PROCEEDINGS OF THE BRITISH ASSOCIATION. 427 



propensities of Dermestes minimus. He believed that the paste was most fre- 

 quently attacked by Acaridce, and the leaves of books by Coleopterous larvre. 

 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 



