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Show 436 MR. J. E. S. MOORE ON THE RESULTS [May 4, necessary, for the moment the peculiar character of its caudal bristles was shown not to be sexual, it was evident that it could no longer be confounded wdth the more normal-tailed species. Adult examples of both sexes were present in the series, as was also the case wdth the Nyasan P. tetradactylus. Mr. Howard Saunders, F.Z.S., exhibited on behalf of Mr. Henry Evans a series of instantaneous photographs, taken in the Outer Hebrides, of the Great Grey Seal (Hallchcerus gryphus) in various attitudes. The following papers were read :- 1. On the general Zoological Results of the Tanganyika Expedition. By J. E. S. M O O R E . [Eeceived April 4, 1897.] The object of this expedition to Tanganyika was to collect materials sufficient for the more complete determination of certain special forms of animals. At the time I started our knowledge of the fauna of the great lakes was in a most imperfect condition. It had been ascertained by Boehm in 1883 that a Medusa inhabited Tanganyika; and through the examination of the empty shells of the various molluscs brought back by travellers from the Interior it had been determined that the great lakes contained examples not only of species and genera wdiich are normal to fresh water, but of others which but for their known lacustrine habitat would certainly have been regarded as marine. It was impossible, however, with the material then at our disposal, to say whether the deviations from the usual characters of the freshwater faunas found in Central Africa were likely to be due to convergence of evolution, I.e. parallel development, or to the lakes having been actually contaminated by oceanic forms. Neither could it be determined, supposing the lakes to have been thus contaminated, whether the marine forms they exhibited were like anything at present existing in the sea, or whether they had persisted or become modified from a more ancient marine stock which has elsewhere disappeared. The probability of these forms having resulted from marine contamination is obviously greatly affected by the question whether they are locally or widely distributed as African freshwater forms. If they are widely distributed, it is quite likely that Africa possesses animals which are not at present known to inhabit lakes elsewhere. If, on the other hand, they are extremely limited in distribution, it is probable that the existence of these enigmatical animals has resulted through the contamination of the great lakes, either in the past or the present, by animals from the sea. In the first place, it wdl be necessary to see if a widespread similarity in the African lake-faunas is in the nature of things possible, and, in order to ascertain this, it is essential to examine |