NA TURE 



[July i, 1597 



In many places the precipitous coast-line of the lake 

 has been canoned out by waves and storm-torrents into 

 a succession of superb rocky headlands, and in the still 

 waters of the recesses, which they partially enclose, there 

 are innumerable swarms of prawns, some of which are 

 certainly Paloemon-like in structure ; but 1 am not yet 

 sure of the affinities of them all. Like those of the 

 Lago di Garda in Italy, lake prawns are generally 

 supposed to have migrated up the rivers from the sea ; 

 but it is curious that they should have found their way 

 2700 feet up into Tanganyika, and yet not have reached 

 Nyasa, which is so much nearer the coast. 



It would be impossible within the limits of this article 

 to give any account of the widely different forms of 

 Tanganyika fish ; but there is a curious and, I believe, 

 quite new example of protective mimicry exhibited by 

 a small chromis, which, in order to escape from the 

 swarms of kingfishers along the shore, has simulated the 

 bands of colour, size, and mode of swimming of a leech. 



There appears to be only one species of medusa in 

 Tanganyika ; but this species, like so many of the lake 

 animals, is subject to wide variation, and if the inter- 

 mediate forms could not have been obtained, the 

 extremes would certainly have been regarded as distinct 

 species. They are rather local in their distribution, and 

 are not always easy to find, but in some places they 

 exist in countless numbers, and are seen at every depth, 

 slowly pulsating after the manner of jelly-fish, till they 

 reach the surface, and then sinking again motionless 

 with their array of long tentacles standing stiffly up above 

 the bell. 



Towards evening the deep water of the lake is often 

 filled with a finely-divided substance, that glitters in the 

 sunshine like precipitated gold, and this appearance is 

 found to be caused by the sculptured shells of swarms of 

 Peridinia, together with a number of large infusoria, the 

 broad bands of cilia and undulating membranes of which 

 show them to be related to the Condylostomas. The 

 appearance produced by this assemblage of pelagic 

 protozoa is probably what Livingstone described in his 

 last journal as a yellow scum on the surface of the lake, 

 attributing it to some vegetable form. 



survivals of an oceanic series that has elsewhere passed 

 away, or that its marine characters are due to parallel 

 development, produced in a fresh-water stock by the 

 action of some conditions obtaining in an immense inland 

 lake. I would at present offer no opinion as to which of 

 these surmises is likely to prove correct ; but whatever sup- 

 position may be entertained, it becomes obvious that the 

 fauna of Tanganyika is comparatively old, for it is unlike 

 anything now inhabiting the sea, and if it is derived from 

 a previous fresh- water stock, much time would be required 

 for the evolution of its widely-divergent present forms. 

 This conclusion as to the comparative antiquity of the 

 Tanganyika fauna is, in my opinion, the most important 

 which can be drawn with certainty from a cursory survey 

 of the facts ; and, without attempting to push comparisons 

 at present, the remarkable similarity between several 

 varieties of Paramelania and those- of the equally variable 

 Jurassic genus Purpurina, between other varieties of 

 Paramelania and the American and Southern European 

 Pirguliferas, should be fully borne in mind. The deter- 

 mination of the actual affinities of the Tanganyika forms, 

 which are often, exclusively related to the lake, can only 

 be made by a prolonged comparative study of the 

 morphology of each, and it would be at present useless 

 to speculate on the result. I have here only indicated 

 some of the peculiarities of the fauna of the lake as they 

 present themselves to a naturalist on the spot, the actual 

 results of the investigation having yet to be produced. 



L E. S. Moore. 



THE LAWRENCE MEDAL. 



'\\JY. are glad to be able to give a reproduction of a 

 * *^ fine gold medal of Sir William Lawrence, now in 

 the Royal Academy Exhibition, designed and executed 

 by Alfred Gilbert, R.A. It forms part of a scholarship, 

 founded in memory of Sir William Lawrence at St. 

 Bartholomew's Hospital, and is given annually. The 

 medal, cast and chased, i\ inches in diameter, shows the 

 face and head in high relief, and gives striking evidence 

 of the artist's skill, as the likeness well preserves the 



The assemblage of animals which I have just described \ 

 appears to be almost entirely restricted to the confines of 

 the lake, and it is this geographical isolation to which at ^ 

 present I would draw attention, as it is, without doubt, ! 

 among the most remarkable characteristics which the 

 fauna possesses. In fact, the presence of such an assem- 

 blage of animal forms in an inland and greatly elevated 

 lake is only intelligible by supposing either that the lake 

 itself was at one time connected with the sea, and that its 

 fauna is a collection of types which have persisted as j 

 NO. 1444, VOL. 56] 



dignity and intellectual power of the original. The view 

 is nearly full face, not the usual profile, a treatment of 

 which there are but few examples, either ancient or 

 modern, and of difficult execution. The reverse has an 

 allegorical subject suited to the aim of the scholarship, 

 and instinct with the grace and fancy of which Mr. 

 Gilbert is master. A youth, full of confidence, presses 

 through the shield dividing him from life, whilst wisdom 

 and science on either hand whisper counsel as they point 

 to the motto on the shield, part of the line from Homer, 



