HORN EXPEDITION — NARRATIVE. 19 



pictiis) and you are all tlie more Kurprisod becauso, if you havo only soon tlicin 

 before in tlio dry season, you wore not at all prepared for sucli a transfoi-niation in 

 colour. Then they were a dull, dirty yellow like the water and the dried up b/mks 

 and vegetation, now they are yellow and orange and green like the water which 

 is thick with yellow sand and mud particles, and dotted with bright green Nardoo 

 leaves. Both these frogs are a fair size, but, in addition to them, there will 

 be found a good many little grey and brown ITylas iyH. rubelln) .sometimes 

 briglitened witli yellow patches, but, on the whole, dull coloured in lioth the wet 

 and dry season. They will be found hopping about on the banks and hiding in 

 damp places under stones and, in addition, hundreds of tadpoles will lie seen 

 which have developed with great rapidity from eggs deposited since the rainfall. 



I am much indebted to Mr. Alexander Sutherland who has ))een good 

 enough to inform me of some of his interesting results recently arrived at in the 

 matter of the varying rate of development of frog eggs at different lemperatures 

 from which we can form some idea of how rapidly the eggs develop in a Central 

 Australian water-hole. 



In a letter which Mr. Suthei-land has kindly allowed me to I'eproduce he 

 quotes the following results of experiments on b.itches of eggs of Ilyla antra 

 consLstini;' of thirteen in each. 



E.XPERI 



WENT A. 





Experiment I>. 



Avera^'e Temp. 



Time. 



Average Tei 



ip. Time. 



2G-G° 



39 hours 



2G" 



48 hours 



25-2° 



- no „ 



■24.,T' 



- 52 „ 



23-9° 



- 59 „ 



23- 



' 5G „ 



22-r 



- 69 „ 



22-2° 



- - 65 „ 



21-5" 



- 73 „ 



21-7° 



- - 67 „ 



In another experiment the average temperature was 30'8" and the time 

 occupied in hatching out was 34 hours ; in another the average temperature was 

 30-7° and the time 34 hours; and in another the average temperature was 287' 

 and the time 37 liours. 



Mr. Sutherland adds " thus if these eggs arc to hatch out in three days the 

 temperature must lie only between 21° and 22". Now, in my pi'csent turtle egg 

 hatching experiments, water kept without artificial heat in a cellar shows a range 

 of only 18-5" to 21° after four days of obsei'vation taken day and night at intervals 

 of three hours. I should not be in the least surprised if the ponds in Central 

 Austi-alia reached 25° as a tolerable average through the summer months in which 



