338 THE POPULAR SCIENCE MONTHLY, 



This habit of lying in the mud and there becoming torpid may be 

 looked upon as a natural alternative to the habit of migrating across- 

 country, Avhen your pond dries up, in search of larger and more perma- 

 nent sheets of water. Some fish solve the problem how to get through 

 the dry season in one of these two alternative fashions, and some in 

 the other. In flat countries where small ponds and tanks alone exist, 

 the burying plan is almost universal ; in plains traversed by large 

 rivers or containing considerable scattered lakes, the migratory system 

 finds greater favor with the piscine population. 



One tropical species which adopts the tactics of hiding itself in the 

 hard clay, the African mud-fish, is specially interesting to us human 

 beings on two accoimts : first, because, unlike almost all other kinds 

 of fish, it possesses lungs as well as gills ; and, secondly, because it 

 forms an intermediate link between the true fish and the fro<rs or 

 amphibians, and therefore stands in all probability in the direct line 

 of human descent, being the living representative of one among our 

 own remote and early ancestors. Scientific interest and filial piety 

 ought alike to secure our attention for the African mud-fish. It lives 

 its amphibious life among the rice-fields on the Nile, the Zambesi, and 

 the Gambia, and is so greatly given to a terrestrial existence that its 

 swim-bladder has become porous and cellular, so as to be modified into 

 a pair of true and serviceable lungs. In fact, the lungs themselves in 

 all the higher animals are merely the swim-bladders of fish, slightly 

 altered so as to perform a new but closely allied office. The mud-fish 

 is common enough in all the larger English aquariums, owing to a 

 convenient habit in which it indulges, and wjiich permits it to be 

 readily conveyed to all parts of the globe on the same principle as the 

 vans for furniture. When the dry season comes on and the rice-fields 

 are reduced to banks of baking mud, the mud-fish retire to the bottom 

 of their pools, where they form for themselves a sort of cocoon of 

 hardened clay, lined with mucus, and with a hole at each end to admit 

 the air ; and in this snug retreat they remain torpid till the return of 

 wet weather. As the fish usually reach a length of three or four feet, 

 the cocoons are of course by no means easy to transport entire. Never- 

 theless, the natives manage to dig them iip whole, fish and all ; and, if 

 the capsules are not broken, the unconscious inmates can be sent across 

 by steamer to Europe with perfect safety. Their astonishment when 

 they finally wake up after their long slumber, and find themselves in- 

 specting the British public, as introduced to them by Mr. Farini, 

 through a sheet of plate-glass, must be profound and interesting. 



In England itself, on the other hand, we have at least one kind of 

 fish which exemplifies the opposite or migratory solution of the dry- 

 pond problem, and that is our familiar friend the common eel. The 

 ways of eels are indeed mysterious, for nobody has ever yet succeeded 

 in discovering where, when, or how they manage to spawn ; nobody 

 has ever yet seen an eel's Qgg, or caught a female eel in the spawning 



i 



