244 A HISTORY OF FISHES 



covers are scarcely apparent. The Tench {Tinea) spends the 

 winter actually buried in the mud, and individuals which 

 were dug up and placed on the bank of a river showed no sign 

 of life until struck smartly with a stick. Fresh-water Eels 

 [Anguilla) generally seek deep water and lie buried in the mud 

 in a torpid condition. Mr. Thompson records that in 1841 

 large numbers of these fishes were killed in parts of Ireland 

 owing to the protracted hard frosts with severe easterly winds, 

 and he describes how their bodies floated down the Lagan to 

 Belfast. Among marine fishes hibernation is practically un- 

 known, but there is reason to believe that young Plaice {Pleuro- 

 nectes) remain in shallow water, and pass the cold period in a 

 quiescent state buried in the sand. 



Aestivation or summer-sleep does not occur among the 

 inhabitants of the sea, but among fresh-water fishes, and 

 particularly among those that inhabit equatorial swamps which 

 are liable to dry up for weeks or months at a time, this is by 

 no means uncommon. Many of the Labyrinthic fishes such as 

 the Climbing Perch (Anabas), Gouramis (Osphronemus), and 

 Snake-heads {Ophiocephalus) , as well as other forms provided with 

 accessory breathing organs, pass the dry season in a torpid 

 condition buried in the mud, emerging again when the rains 

 once more fill their ponds and streams. The natives of some 

 parts of India obtain a regular supply of fresh fish by digging 

 up the Climbing Perch with a shovel. 



Among the Lung-fishes {Dipneusti) more elaborate prepara- 

 tions are taken for avoiding death during the dry weather. 

 The Mud-fishes or African Lung-fishes (Protopterus) live in 

 streams and small rivers which may be absolutely drained for 

 lengthy periods, and their mud beds baked hard by the tropical 

 sun. As the dry season approaches, each fish burrows down 

 into the mud, and the copious slime secreted by its skin mixes 

 with the mud and forms a hard cocoon in which the fish lies 

 dormant until the next rain. A small passage leading from the 

 inside of the prison to the exterior enables it to breathe air 

 during the period of incarceration. From time to time some 

 of these cocoons have been dug up and sent to Europe, and, 

 even after a period of six months, when one of these was placed 

 in tepid water the coating of mud dissolved away and in a 

 few minutes the captive fish was swimming about freely in the 

 water. The South American Lung-fish (Lepidosiren) constructs 

 a somewhat similar burrow in the mud, but leaves an opening 

 to the exterior, which is closed by a porous lid of clay. 



