he Kai's 
A PERCY SLADEN TRUST EXPEDITION. 
which are capable of being dispersed across the surface of the ocean. It is too early as 
yet to prophesy how far we shall realise the first of these anticipations, although we did 
find traces in the Seychelles of the existence of an infinitely larger fauna than occurs at 
present. The second anticipation proved true, and we hold large collections from the 
islands of the Chagos Archipelago, from Coetivy, and from other places, which we trust 
will throw light on the methods by which oceanic islands receive their population. An 
ideal type of locality for such a study would be an oceanic island, whose neighbouring 
continents have had their faunas and floras thoroughly well described. In the 
Atlantic such islands as exist are open to the suspicion of former connection with 
continents, while the organisms of the oceanic islands of the West Indies have been too 
much changed by man for any accurate estimate to be possible of the causes of their 
distribution. The Pacific is a vast ocean and the organisms of its surrounding 
continental lands are but little known. The Indian Ocean, therefore, seemed to be 
the most suitable, and it was felt that special attention should be paid to the question. 
As another point bearing on the above questions, we studied the interrelations of 
fauna to flora, and of both to the soil, and other features of the environment. In this 
we were aided by our own experimental studies in the Maldives and Minikoi. Each 
generation of mankind may be expected to improve on the work of its predecessors, and 
our own studies on this, the foundation problem of distribution, must themselves be 
regarded as purely tentative and solely of utility in pointing out lines along which 
future work may proceed. 
We now turn toa fresh problem in distribution, the question of the dispersal of 
marine organisms through the water of the globe. The factors in“ eration here are 
currents, tides, food, the possession of swimming larvee, and the power of living at 
varied ranges of depth, whereby deep-living forms can ascend or descend the submarine 
slopes in order to migrate into new grounds. We know that the deeper seas contain 
animals of wide distribution and great similarity. Of these most forms are confined 
to deep water, though we do get striking anomalies in vertical range, such as in the 
genus Proneomenia found by the ‘Siboga’ from 18 to 3088 metres, from 27° C. 
to 2:9° C.* 
When we actually come to examine the question, we find that we do not know where 
shallow-water faunas end and the deep begin, or whether they gradually merge into one 
another. In going through the work of the many expeditions since the ‘ Challenger,’ 
we were struck with the relative paucity of observations under this head and by 
the scarcity of dredgings, from which information might be expected. Even the 
depth to which marine plants could live seemed uncertain. Taking these points into 
consideration, we decided to confine our dredging to the examination of moderate depths, 
especially areas from 50 to 300 fathoms. To this end we had arranged to spend 
at least two months in the Chagos Archipelago, a place from which especially good 
results were to be expected on account of its isolated situation. But to our dismay we 
were prevented in our designs, as our dredge-wire did not reach us till after our arrival 
at Mauritius. From there we still had a large stretch of ocean to traverse, and time 
* «Introduction et Description de ]’Expédition,’ par Max Weber, p. 120. 
