126 BAHIA BLANCA. 



and geraniums ; and the birds began to lay their 

 eggs. Numerous Lamelhcorn and Heteromerous 

 insects, the latter remarkable for their deeply sculp- 

 tured bodies, were slowly crawling about ; while 

 the lizard tribe, the constant inhabitants of a sandy 

 soil, darted about in every direction. During the 

 first eleven days, whilst nature was dormant, the 

 mean temperature, taken from obsei'vations made 

 every two hours on board the Beagle, was 51° ; 

 and in the middle of the day the thermometer sel- 

 dom ranged above 55'^. On the eleven succeed- 

 ing days, in which all living things became so ani- 

 mated, the mean was 5S°, and the range in the 

 middle of the day between sixty and seventy. 

 Here, then, an increase of seven degrees in mean 

 temperature, but a greater one of extreme heat, 

 was sufficient to awake the functions of life. At 

 Monte Video, from which we had just before sail- 

 ed, in the twenty-three days included between the 

 26th of July and the 19th of August, the mean 

 temperature from 276 observations was 5S°-4 ; the 

 mean hottest day being 65°*5, and the coldest 46°. 

 The lowest point to which the thennometer fell 

 was 41°-5, and occasionally in the middle of the 

 day it rose to 69° or 70°. Yet with this high tem- 

 perature, almost every beetle, several genera of 

 spiders, snails, and land-shells, toads and lizards, 

 were all lying torpid beneath stones. But we have 

 seen that at Bahia Blanca, which is four degrees 

 southward, and therefore with a climate only a very 

 little colder, this same temperature, with a rather 

 less extreme heat, was sufficient to awake all or- 

 ders of animated beings. This shows how nicely 

 the stimulus required to arouse hybernating ani- 

 mals is governed by the usual climate of the district, 

 and not by the absolute heat. It is well known that 

 within the tropics, the hybernation, or more prop- 



