Freshwater Crustacea of the Indian Archipelago, 243 



immigration is still taking place at the present time, and that 

 it sliows us the process of the formation of the freshwater 

 fauna *. 



I should like to prove this by means of the Crustacean 

 fauna of the freshwaters of the Indian Archipelago ; for mj 

 material bearing upon this question is already accurately 

 worked out, and was collected by myself with my own hands, 

 with the exception of the Crustacea of Timor and E,otti, for 

 which I am indebted to my fellow-traveller Prof. A. 

 AVichraann, of Utrecht. Since, however, the latter was well 

 acquainted with the questions which interested me, I have 

 before me absolutely precise statements with reference to the 

 origin of these specimens also. The latter point is of 

 paramount importance in this question, in which we have to 

 consider the nature of the water, whether fresh, brackish, or 

 sea-water, in which the animals were collected. 



If the specimens were obtained in the lower course of a 

 river, it is necessary to notice whether any and what change 

 takes place in the water in that portion of the stream at flood- 

 tide. Close attention was paid to all these points. 



Now since such observations were not, or not to a sufficient 

 extent, connected with the Crustacea previously collected in 

 the Indian Archipelago, I was hardly able to derive further 

 statements from the literature on the subject. A solitary 

 exception is constituted by the excellent communications of 

 E. von Martens, to whom altogether we owe the most 

 comprehensive and best information, not merely for the 

 Indian Archipelago, upon this subject. For the rest I depend 

 exclusively upon my own experience. 



The following list of the freshwater Crustacea of the Indian 

 Archipelago gives at once statements as to their occurrence 

 in the different islands: — Sumatra (S.), Java (J.), Borneo 

 (B.), Celebes (C), Saleyer (Sal.), Flores (F.), Timor (T.), 

 and the Moluccas (M.) ; as also as to their occurrence in 

 fresh, brackish, or sea-water, or upon the land in damp 

 surroundings. 



Certain species, which are absent from my collection, and 

 as to which I have no personal experience, are indicated by 

 spaced type. The statements in brackets — ( ), [ ] — as to 

 occurrence imply that the observations in question do not 

 emanate from me. 



This list will be followed by a few remarks and conclu- 

 sions, as well as by a description of the Argulidaj, Isopoda, 

 and Amphipoda which I collected. 



* With regard to tliese questions, I consider it my duty to remind the 

 reader of the valuable but largely forgotten paper by Eiitimeyer — 

 'Ueber die Herkunft unserer Thierwelt,' 1867, p. 17. 



