162 
HORN EXPEDITION—AMPHIBIA. 
the dry season. In the following January and February several water-holes in 
the same district were swarming with them, in various stages of development. 
They were not present in, by any means, all the water-holes, being found, 
presumably, only in those by the sides of which the adults had been restivating. 
Their distribution is undoubtedly influenced largely by the periodicity of the 
rainfall. It will make, for example, a very considerable difference whether during 
one season one or more falls of rain occur ; if only one fall takes place, then the 
creeks x’apidly dry up, and the tadpoles which are developed subsequently are 
confined to the water-holes in which they happen to have been developed, as the 
creeks will only run for perhaps a very few days, and so the water-holes ai’e rapidly 
isolated. If, after the tadpoles have developed to a certain stage a second rainfall 
takes place, then they will be carried away to stock other water-holes, by the side 
of which they will in their turn aestivate when the dry season returns. 
By far the greater number of tadpoles never attain maturity. In addition to 
extermination by their natural enemies, as can be seen any time when the shallower 
parts of water-holes begin to dry up, numberless tadpoles ai’e killed which have not 
had time enough to develope to the youngest stage at which they can begin to 
burrow and thus are enabled to ajstivate. 
They must, if they are to survive, develope rapidly, and side by side in the 
same pool, within two weeks of the rainfall, will be found tadpoles of the smallest 
size, together with those in which the hind limbs are large, and others in which 
the front limbs have also appeared and the tail is beginning to dwindle. It is, 
as before stated, only those which develope the most rapidly which have any chance 
of surviving under the ordinary conditions of life in Central Australia. 
The following are the dimensions of the tadpoles :—Length of body about one 
and a half times the width and about two-thirds the length of the tail; nose some¬ 
what nearer to the tip of the snout than to the centre of the eye ; eyes on the 
upper surface not visible from below ; the spiraculum is on the left side, not very 
prominent, and not visible from above. 
The anus opens at the end of a tubular projection lying to the right side of 
the ventral crest and projecting backwards beyond the base of the tail. This 
tubular projection is longer relatively in the smaller than the larger tadpoles. 
The tail is about half as long again as the body, the upper crest thins away at 
the base of the tail, the lower crest is united anteriorly with the tubular projection 
at the end of Avhich is the anus. 
