S10 FISHES CHAP. 
ditions, there can be little doubt that its value as such is much 
greater whenever gill-breathing becomes difficult or impossible. 
This seems to be the case during the hot season, when the water 
becomes foul from the presence of decomposing animal or vegetable 
matter. Semon records a striking illustration of this in the 
case of a partially dried-up water-hole, in which the water had 
become so foul that it was full of dead fishes of various kinds. 
Fatal as these conditions were to ordinary Fishes, Neoceratodus 
not only survived but seemed to be quite healthy and fresh. 
Such observations are of exceptional interest. Not only do they 
afford a clue to the conditions of life which, in the course of 
time, probably led to lung-breathing in Neoceratodus, but they 
also suggest the possibility that a similar environment has been 
conducive to the evolution of air-breathing Vertebrates from gill- 
Fic. 305.—A young Neoceratodus four weeks after hatching. c, Cloacal aperture ; 
1.1, lateral line ; m, mouth ; op, operculum ; p.f, pectoral fin. (From Semon. ) 
breathing and Fish-like progenitors. In spite of its pulmonary 
respiration, Neoceratodus more closely resembles the typical Fishes 
in its habits than any other Dipneusti. It lives all the year 
round in the water. There is no evidence that it ever becomes 
dried up in the mud, or passes into a summer sleep in a cocoon, 
and the well-developed condition of its gills suggest that these 
organs play a more important role in breathing than in either 
Protopterus or Lepidosiren. The Fish is not known to leave the 
water, and the paired fins, useful no doubt as paddles, are quite 
incapable of supporting the bulky body on terra firma. In fact, 
when Neoceratodus is taken out of its natural element it seems 
to be more helpless than most other Fishes, and, in spite of its 
capacity for lung-breathing, soon dies unless kept moist by 
artificial means. Spawning takes place from April to November, 
principally in September and October. The eggs, invested by 
a jelly-like coat, secreted by the oviducal walls, are deposited 
