258 



DIPNOI. 



lies with the body bent and the tail folded over the face, and 

 surrounded by a cutaneous secretion of mucus containing earthy 

 particles. The outer layer of this mucus which is in contact 

 with the earth of the burrow hardens and constitutes the cocoon 

 or capsule. The upper end of the capsule is closed by a kind 

 of lid, on the surface of which is an aperture leading into a pipe 

 of dried mucus which passes between the lips of the animal 

 (Fig. 135). As the water diminislies the animal ceases its 



branchial respiration and the 

 earth.t luug rcspiratiou alone con- 



tinues. Lepidosir €71 lies at 

 the bottom of its burrow sur- 

 rounded by mucus, but there 

 does not appear to be a 

 special cocoon with lid and 

 pipe as in Protopterus. 



Breeding takes place shortly 

 after the return of the Avater 

 and the liberation of the animal 

 from the mud. This varies 

 considerably in accordance with 

 the season. Lepidosireii lays 

 its eggs in underground bur- 

 rows, which after descending 

 vertically about one foot run 

 horizontally for two to five 

 feet. The male remains in the 

 nest with the eggs in a curled 

 up position. 



All three genera take 

 both vegetable and animal 

 food. 

 The Dipnoi may be divided into two sub-orders or families. 

 One of these — the Sirenoidei — includes the living genera and 

 numerous fossil teeth, which are found only in the Jurassic and 

 Triassic formations and on which the genus Ceratodus was 

 originally founded. The bulk of the Dipnoi are, however, 

 exclusively Palaeozoic forms. It is a noteworthy fact that the 

 genus Ceratodus which existed in Triassic and Jurassic times 

 has persisted to the present day, though no remains of it or of 



Fig. 135. — Diagram of tlie torpid Protopterus 

 in situ (after W. N. Parker). The tube is 

 open above, and the cocoon lies in the 

 bottom of it The pipe is shown leading 

 into the mouth, coc cocoon ; earth earthy 

 mass round cocoon ; earth, t burrow through 

 earth ; Id hd of cocoon : Id. p pipe from lid 

 of cocoon ; pel pectoral fin ; pl.l pelvic 

 fln; tl tail. 



