1906.] AUSTRALIAN LUNG-FISH. 171 



axil. The eye shows a distinct greyish line within the orbit : it 

 is somewhat dull in colour and the iris brown. The scales appear 

 most prominently when the fish exhibits an undulating movement, 

 their lighter-coloured proximal rims, usually covered by the 

 neighbouring scales, then becoming exposed. 



In its movements the fish suggests an amphibian : it will lift 

 its head from the bottom, raising itself upon the bases of its pectoral 

 fins and will thus pose for several minutes. In this process it 

 exhibits occasionally neck-movements which are distinctly unfish- 

 like. Sometimes it will then push itself back in a way which has 

 been noted in the African Lung-fish, Protopierus. In general, 

 however, the movements of the fish in swimming are more ganoid- 

 like than in the latter form. It swims leisurely about the aquarium, 

 undulating the body and balancing with the pectoral fins, thus 

 operating very much like those of the living Ganoids. In more 

 energetic movement it will sometimes show the pectorals fluttering 

 above the head as it rapidly raises and depresses them, the tips of 

 the fins being flexible. There is, however, less tendency for the 

 alternate movements of the pectoral fins ; this, in fact, was rarely 

 observed, and there was very little movement noted in the ventral 

 fins : they are, therefore, far more passive than in Protopte7'us. It 

 was observed on some occasions, when the fish was swimming near 

 the surface, that it would suddenly cease its movements and slowly 

 sink (horizontally) to the bottom, its fins extended at the sides, 

 acting as parachutes. When alarmed, on the other hand, it is 

 capable of vigorous movements, sweeping forward by strong strokes 

 of its caudal, the pectorals and the ventrals folded tightly against 

 the body, very much, as Semon remarked, as in the case of a 

 rapidly swimming amphibian. 



The best idea of the usual movements of Ceratodus may perhaps 

 be had by reference to the accompanying figures, which have been 

 copied from pencil sketches. 



The aquatic respiration of Ceratodus is normally slow and 

 regular : the opercular cavity fills and empties about twelve times 

 a minute, and during the process it may be observed that the movith 

 is scarcely opened. Occasionally, however, it will open its mouth 

 and "gasp" spasmodically. It is clear, however, that the fish is a 

 nostril-breather. The mouth itself shows no movement of opening 

 or closing ; it is indeed hardl}^ open, the gape being scarcely more 

 than 3 millimetres. The nostrils, on the other hand, are 

 widely dilated, and on one occasion a twitching was observed, 

 which was by no means fish-like. It was also noticed that the 

 aquatic respiration became more rapid after the fish had become 

 excited, e. g. after it had been pushed about the tank in order to 

 be photographed ; the number of respirations then became as 

 numerous as thirty in the minute. 



Breathing by means of the lung takes place at considerable and 

 somewhat irregular intervals : from forty to sixty minutes would 

 include the usual periods. When excited, however, the fish 

 breathes more rapidly, and on one occasion the interval of aeiial 



