CONTENTS. 
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CHAPTER I. 
INTRODUCTORY. 
PAGE 
Reasons for acquiring a better knowledge of the fauna of the Great African Lakes — 
Our first knowledge of the existence of unique animals in Tanganyika arose as a 
by product of Burton’s journey — The shells collected by Speke on Tanganyika 
were marine in aspect — But the shells obtained from the other African Lakes 
were not so — Extension of our knowledge of the Tanganyika shells — Possibility 
of the lake having been connected with the sea — Intensification of the interest 
in the Tanganyika problem produced by Boehm’s discovery of jelly-fishes — • 
Formation of the first Tanganyika expedition — As a result of this it is shown 
that the Tanganyika problem is larger than was supposed — Conflict between 
the zoological evidence and geological anticipations — Erroneous character of 
Murchison’s geological speculations — Actual impressions of the African in- 
terior — Remarkable character of the Halolimnic shells of Tanganyika — Their 
similarity to those of the Jurassic seas — This comparison a possible solution of 
the Tanganyika problem — Insufficiency of our knowledge of the Great African 
Lakes — Suess’ views — Possibility of a former extension of the sea into Tan- 
ganyika from the north — Geological and geographical interest of the country 
north of Tanganyika — Formation of the second Tanganyika expedition — 
Arrangement of matters contained in the present work ..... I 
CHAPTER IE 
ON THE NATURE AND ORIGIN OF FRESH-WATER FAUNAS AND THEIR 
RELATION TO THE FAUNA OF THE SEA. 
Animals live in fresh-water which do not inhabit the sea — Animals live also in 
brackish water — It is generally accepted that fresh-water organisms have 
arisen from marine forms and have colonized fresh-waters from the ocean 
— Recent additions to our knowledge of fresh-water faunas — Beaudants’ experi- 
ments — Views of Semper Sollas and Von Martens — Apparent impossibility of 
many marine organisms eyer getting into fresh-water — Inadequacy of existing 
views respecting the nature of fresh-water faunas — Similarity of fresh-water 
faunas all over the world — Distinction of primary and secondary fresh-water 
stocks — Origin of the second obvious, of the first not so clear — Ancestral 
