128 Ml{. J. S. BUDGET! ON THE 



dart backwards from the surface. When the young Gijinnarcluis leaves the nr^st it has 

 fully developed the characteristic cylindrical tail of the adult, and in this connection 

 its habits are very interesting. 



The Gymnarchus propels itself through the water, not by the action of its paired fins, 

 not by the motion of its tail or the undulatory motion of the axis of its body, but 

 entirely by the action of its dorsal fin. This fin extends nearly the whole length of the 

 dorsal surface, ceasing abruptly at the commencement of the cylindrical tail. When 

 Gymnarchus starts forwards, the motion is the result of a series of waves passing 

 backwards along the dorsal fin. About five such waves are passing at a time. 

 Suddenly the fish will proceed at the same rate in the opposite direction, and now the 

 motion is the result of a series of waves passing forwards along the dorsal fin. 



As the Gymnarchus swims rapidly backwards in this way, it may be seen to guide 

 itself through the grasses by using this peculiar tail which it possesses as a feeler. 

 Thus it appears to be quite immaterial to the fish which way it progresses, and it 

 always appears to swim in comparatively straight lines. 



How Gymnarchus constructs the wonderful floating nest in which it lays its eggs I 

 have been unable to observe. The natives approach these nests with great caution, 

 statir.g that the parent is at this time extremely fierce and has a very formidable bite. 

 Both the adult fish and its eggs are greatly sought after as food. 



A large number of the young fry of Gymnarchus, which I had caught immediately 

 they left the nest, lived well on chopped-up worms. I tried to bring some of them to 

 England alive, but every one died as we got into colder climes. 



V. — The Nesting- habits of Heteeotis niloticus Cuv. 



In the same swamps, during the month of July, a most striking feature is the 

 presence of numbers of enormous nests, which proved to be those of Heterotis niloticus 

 (text-fig. 21). These nests measured four feet in diameter, and were made in about two 

 feet of water. In wading through the reed-choked swamp, when one came across one 

 of these structures they appeared like miniature lagoons. The walls of the nest were 

 about eight inches thick at the top and compact, being made of the stems of the 

 grasses removed by the fish from the centre of the nest. The floor of the nest was 

 the swamp-bottom, and was made perfectly smooth and bare. 



Once I watched a " Fantang," as the natives call this fish, making its nest. It was 

 circling round and round the wall of its nest, every now and then throwing its tail 

 upwards and outwards, tossing on to the top of the wall the debris from the inside of 

 the nest. Thus it toiled on until the wall reached the surface of the water and was 

 complete. When the nest was finished, the water it contained was perfectly clean and 

 clear, so that I could see with my water-telescope the eggs nearly covering the bottom 

 of the nest. When all the eggs are laid, the fish leaves the nest by a hole at one side. 



