MODES OF REPRODUCTION 319 



the surface of the membrane may be smooth and hard or ad- 

 hesive or provided with long filaments. 



Of the three surviving genera of lung-fishes (Dipnoi) Cera- 

 todus lays its eggs separately and singly among the water-weeds 

 and takes no care of them. This fish lives only in the Burnett 

 and Mary rivers of Queensland, and these rivers never entirely 

 dry up, although in the hot season they are reduced to a series 

 of stagnant water-holes connected by shallow channels where 

 the water has almost disappeared. Protoptems lives in the 

 shallow swamps of West Africa, and passes the dry season in 

 holes in the mud, the fish being being enveloped in a cocoon 

 formed of hardened mucus secreted by its skin. This aestiva- 

 tion takes the place of the hibernation of our common Amphibia, 

 the latter being due to the winter cold while the former is the 

 result of heat and drought. In both cases reproduction follows 

 the period of torpor. When the swamp has been again flooded 

 by the rains after the dry season Protopterus makes near the bank 

 a nest consisting of a hole in the mud about a foot in depth, 

 filled with water and surrounded by the long grasses. It is 

 probably the male which makes the nest, for he remains in the 

 hole guarding the eggs which are deposited by the female on 

 the bare mud at the bottom. Like other male fishes which ex- 

 hibit parental instincts the male Protopterus protects the eggs 

 from two kinds of danger, that of being devoured by other ani- 

 mals and that of death from want of oxygen. He bites viciously 

 at any living creature which intrudes into the nest and he keeps 

 the water aerated by lashing movements of his tail. The South 

 American Lepidosiren has somewhat similar habits, our know- 

 ledge of which is due chiefly to Professor Graham Kerr who 

 made two expeditions to the Chaco Boreal, west of the upper 

 part of the River Paraguay, for the purpose of investigating the 

 breeding and development of this lung-fish. Lepidosiren, like 

 Protopterus, breeds at the beginning of the rainy season, making 

 for its nest a new burrow distinct from that in which it aestivated. 

 The nest-burrow differs from that of Protopterus in being much 

 longer and in the fact that it consists of two portions, a vertical 

 portion extending about a foot from the surface and a hori- 

 zontal part from a foot to four feet in length. At the end of 

 this burrow the eggs, which are similar to those of Amphibia, 

 are laid by the female, and as in the case of Protopterus the male 



