THE AUSTRALIAN LUNG-FISH. 609 



inch annually for the last thirteen years. At this rate the present 

 fishes are over forty years old, and a fish of the record size 

 (45 inches) would be over sixty. But this assumes that the rate 

 of growth in length is approximately unifoi-m in fishes of different 

 ages. In point of fact it is known that fishes in all groups grow 

 quickly when young, and slowly, if at all, when old : it is also 

 known that under favourable conditions a fish may grow with 

 far greater rapidity. In the case of Ceratodus the rate of growth 

 of the young is as follows : — 



Length of specimen. -^ffe. 



inches 



r\ At hatching. \ 'Notes from stages 



J^ " reared in balanced 



y# ^ month. > aquaria in Gayndah, 



9 1 3 mnntli Queensland, by Mr. 



16 ^4 month. J Thomas Illidge.) 



i^ 2 months. 



1 2}j months. 



Ig 6 months. 



1^ 7 months. 



2^^ 7i months. 



2f 8 months. 



In stages lately hatched the growth is seen to be rapid, its 

 rate suggesting that a specimen 12 inches in length might be 

 not older than a year. The rate, however, changes notably when 

 the young fish no longer subsists on its yolk. In fact, for a 

 period of about two months it actually decreases in size, a state 

 of affairs, however, probably abnormal and due to the lack of 

 proper food in the aquarium. Young an inch long are nine 

 weeks old ; young two inches long are over seven months old. 

 At the end of the first year the young Ceratodus measui"es, we 

 infer, about five inches, a rate of growth which would be not 

 unlike that in young ^«w'a, gar-pikes, or in a number of teleostean 

 fishes. If the analogy with known ganoids continues, a two- 

 years' Ceratodxis would measure 8-9 inches ; and a specimen 

 25 inches in length, approximately the size of one of the present 

 fishes when it appeared in London, is estimated to be from eight 

 to ten years old; this added to the thirteen years of their 

 living in the Society's aqviarium, makes the total age of the 

 present specimens between, roundly, twenty and twenty five 

 years. Older and larger specimens it is fair to credit with 

 great age, probably fifty years. 



Breathing. — The aquatic respiration of Ceratodus varies con- 

 siderably according to the temperature of the water, but its range 

 has not been observed. In September (1904), on a cool day, 

 with water temperature not far from 65° Fahrenheit, the respi- 

 ratory movements were " slow and regular ; the opercular cavity 

 filled and emptied about twelve times a minute." In late 

 June, when the water temperature was nearly 75°, the successive 



