ditch-like channels having been dug to furnish depths 

 carrying from 3 feet to 4J feet of water where the young 

 fish may retreat for safety upon any sudden atmospheric 

 change. In the shallows of the entrance ponds flourishes 

 a luxuriant growth of marine and brackish water vegeta- 

 tion, chiefly confervae and a species of marine flowering 

 plant {Ruppia maritima) which finds here extremely 

 congenial conditions. The marine prairie thus formed 

 over the shallow central portion of each pond is the 

 home of swarms of minute life — infusorians, zoophytes, 

 and small crustaceans and molluscs, constituting the main 

 food supply of the young fishes. The great majority of 

 these fish-farms and all the large ones have separate 

 wintering ponds where the fish are herded during cold 

 weather. These are deep canal-like ponds of sinuous 

 course, sometimes over a mile in length by 20 to 30 feet 

 in width. As a long length is required the course 

 doubles upon itself so often that it becomes a veritable 

 maze. These wintering channels are situated in the 

 most sheltered section of each property and care is taken 

 when excavating them to pile the material dug out as a 

 protective embankment along the north-east and south- 

 east boundaries as a protection against the cold winds 

 which blow from these directions ; as a further protec- 

 tion these banks are often planted with thick hedges of 

 tamarisk, a plant that thrives well on the coasts of 

 Western Europe. 



Construction of Sluices. 



The general plan and arrangement of the sluices 

 which place the ponds in communication with Arcachon 

 basin vary very slightly in the different farms ; the 

 dimensions which follow are those of a sluice on 

 M. Garnung's property and they and the accompanying 

 plans (text-figs. 1 to 3) and photographs (figures 1 to 5) 

 of sluices on the same farm may be considered as typical 

 of the form in accepted use. The differences which 

 exist are chiefly in the materials employed and in the 

 mechanical details of the means employed to raise and 

 lower the sluice shutters. 



The sluice now to be described is one leading into 

 the principal entrance pond. It consists of a cutting 



