THE VICTORIAN NATURALIST. 21 



known as a swim-bladder, which is merely a long hollow process 

 developed from the oesophagus. This serves, probably, mainly 

 as a float, and not at all for respiratory purposes ; but in the 

 small group, Dipnoi, of which Ceratodus is one, this same swim- 

 bladder becomes modified to act as a lung. Not only this, but, 

 whereas in fishes the impure blood which is carried from the 

 body to the heart passes to the gills, is purified there and then 

 goes straight to the body, in the Dipnoi part of the blood goes 

 from the heart to the lung and then is carried back again to a 

 chamber in the heart specially developed for its reception. In 

 fact, in the Dipnoi we can see some of the earliest stages in the 

 evolution of important organs of the body as we now find them 

 in all animals above fishes. 



At the present time only three examples of the Dipnoi are 

 known to exist in the world — one form, Lepidosiren, lives only 

 in the Amazon ; another, Protopterus, is only found in tropical 

 Africa ; and the third, Ceratodus, occurs only in the Burnett and 

 Mary Rivers, in Queensland. In past times, however, Ceratodus 

 lived in other parts, such as Europe, as its fossil remains testify ; 

 and in Australia Professor Tate has recorded the presence of 

 its teeth in the strata of the Lake Eyre basin. In fact, 

 Ceratodus is one of those rare forms of which fossil remains 

 were found and named before the living form was discovered. 



The habits of Protopterus have been studied, and it is stated 

 that during seasons of drought it makes a cocoon of mud for 

 itself, and breathes by means of its lung. On account of this 

 habit, these forms have often been called mud and lung fishes. 



My main aim, then, was to find the eggs of the Ceratodus. 

 From Mr. Caldwell's published notes, which are only too brief, I 

 knew that it deposited them much like some amphibians such as 

 the Axolotl do, on weeds, and that he had found them in Sep- 

 tember. 



To return now to Gayndah. I purchased a tent and provi- 

 sions, and having hired two boys accustomed to the river, started 

 away to camp out some few miles up the Burnett. The country 

 was very dry and sandy, with all the creeks empty of water. 

 The outcropping rocks are granitic, with basalt capping the hills 

 around, and the disintegration of the granite appears to give rise 

 to a vast amount of sand. Along the river itself there is an 

 alternation of large sandbanks, where the stream is shallow, and 

 of long deep pools with great granite masses. The banks are bor- 

 dered by Bottle-brush Trees (Callistemon), which at that time were 

 crimson with flowers, and alive with Thickheads. Leaving my 

 stores to find their way to an appointed spot, I kept by the river 

 bank on the look-out for weeds, for without these it was hopeless 

 to set to work. After a short halt at a station close to Mt. 

 Debatable, where the Sociable Wasp (Polistes ferrugineus) was 



