page 42
SHELLS (FRESHWATER), REMARKS ON THE STUDY OF.
BY THE REV. J. E. TENISON WOODS, F.G.S., F.L.S.,
[Read 9th August, 1875.]
[This is a transcript of Rev. Tenison Woods further general comments about freshwater shells of Tasmania. It starts at the last para on page 42, and finishes at the end of the first para on page 43.]
The Rev. J. E. Tenison WOODS, F.G.S., F.L.S., read a paper on the Freshwater shells of Tasmania, prefacing it by some remarks on the study of fresh water shells generally. "It must not be supposed," he said, "that such studies meant no more than merely naming certain specimens new to science. To the outside public it might seem no more, but to the man of science it was different. A name when applied to a new species thenceforth became not only a tally by which it might be known and referred to, but it meant all the details of observation in its description, and it was a centre around which a multitude of useful observations would be grouped. Thus Scalaria Australis is a name applied to a marine shell of a peculiar, and at one time, rare genus. Other naturalists had found that its habits were most interesting and various. Thenceforth the name was the repository in which those observations were collected, and they were conveyed to the mind of those familiar with them by the mere association of the name. Finally the same mollusc had been found to contain a beautiful purple dye, and this also became, if we may so speak, a property of the name. All natural science is more or less open to the reproach that it is a science of names, but this would also be strictly true of all human knowledge, since it is only by names or words that it can be
page 43
communicated. The fresh water shells did not present a very inviting field to the naturalist in the early history of science, but they were not long studied before they were found to possess features worthy of attention. A great impetus had been given to the study by Mons. Draparnaud, a young French surgeon, whose brilliant career was stopped all too soon by the insiduous ravages of consumption. His work forms a standard on the subject, as it is a model of accurate observation, careful delineation, and charming interest. It was owing to the knowledge thus given that the eminent osteologist Baron Cuvier was so much aided in his determination of the fossils of Montmartre, Paris. There bones were found associated with shells, and the bones might have been supposed to belong to marine drift, but an attentive consideration of the shells showed them to be fresh water, and of a kind whose habits of life were now known. This tended materially also to explain the conditions under which the extinct mammals of the bed existed. Much light had been thrown on the conditions of life in the coal formation from the freshwater and land shells found embedded in it. The reverend gentleman went on to describe generally the natural history of that order of Molluscs known as Pulmo-branchiata, that is Molluscs with lungs and gills, breathing both air and water. Water is their natural element, but they can also live out of it. As they live in creeks and waterholes, which are liable to diminish or totally dry up in certain seasons, they must have means for withstanding a drought, or the order would soon perish. They are therefore provided with an apparatus which is part lung and part gill. The organ is a respiratory sac through which the blood flows, and is aerated in a network of minute vessels, and it is filled with branchial plates or lamellae for the purpose of extracting the necessary oxygen from water. He called attention to the observation of Draparnaud, who said that if we consider the very small number of points by which the animal is attached to the shell, one is astonished to understand how so fragile a covering could withstand the action of external agents, and at the same time preserve its solidity, its colour, and its transparency, especially as upon the death of the animal it bleaches and exfoliates on slight exposure. We must then admit some sort of intercommunication between the shell and the animal which it encloses. We must admit also that it is animated with vitality, although it appears to our eyes, which are too feeble to unravel its interior structure, as if it were mere inert matter." The reverend gentleman then read the introduction to his paper.