36 N. Annaxdai.k : The Fauna of Brackish Ponds. [VoL. I, 



contained logs of wood to which the animal could attach itself^ 

 and now these logs are no longer to be found, either in the 

 pond which is nearest to the railway station or in any other in 

 the neighbourhood ; they have evidently been removed by human 

 agency or else have rotted awa}'. The bottom of all the ponds now 

 consists of soft mud, which is devoid of any hard substances 

 except an occasional twig, small tree-stump, or brick, and as there 

 are very few trees in the vicinity, twigs are rare and tree-stumps 

 still more so. The bricks are also scarce, being derived from 

 ruined drains and wells, and there are no stones in this part 

 of Bengal. The ponds are all shallow (probably at no point more 

 than ten feet deep when full) but the depth of the mud at their 

 bottom is considerable. It is black beneath the surface, contains 

 a large amount of organic matter and smells foul when disturbed. 



The flora of the ponds consists chiefly of filamentous and uni- 

 cellular algse ; but in some cases two or three species of Phanero- 

 gams occur, notably at least two of Naias, a duckweed and a true 

 water-lily, the last being rare, the first abundant in some of the 

 ponds. 



An important factor in the environment is the nature of the 

 water. I have described the ponds as brackish, but at some time of 

 the year the water may contain the same proportion of soluble salts 

 as the sea, at others it may even be more strongly saline, and 

 again at others it is much more nearly fresh. As a rule the ponds 

 are completely isolated both from one another and from the 

 estuary. During the cold weather they are exposed to evaporation, 

 which becomes intensified during the hot weather. During the rainy 

 season, on the other hand, they become filled up with fresh water 

 and probably often coalesce. They are also liable to be placed in 

 temporary communication with the estuary occasionally, owing to a 

 flood bursting the embankment ; but this does not occur b}^ any 

 means every 3^ear. When it does happen, it happens owing to the 

 estuary being swollen with fresh water, which is flowing down from 

 up-country ; so that the ponds, even under these conditions, are 

 practically cut off from the .sea. 



Stoliczka, apparently in 1868 or 1869, had the water of the 

 ponds anal^'sed ; but he does not say at what time of year his samples 

 were obtained. He found that the proportion of soluble solids 

 was 1 2 '87 per thousand, sea- water containing from 32 to 39 per 

 thousand. Mr. D. Hooper, Curator of the Industrial Section of the 

 Indian Museum, has kindly examined samples taken b^' myself in 

 December and March last. Two samples came from a pond in 

 which the Hydrozoon Irene ccyloncnsis , as well as the Actinian, 

 was reproducing its species, and in which the plant Naias was 

 abundant. A sample taken from this pond at the beginning of 

 December, a few weeks after the end of the rainy season, was found 

 to contain 12*13 per thousand of soluble salts, while another taken 

 on March 17th contained 20"22 per thousand. At the latter 

 date water from the edge of the Matla at Port Canning contained 

 25 "46 per thousand, and that from a second pond near the first 



