116 



BAHIA BLANCA. 



Aug. 1833. 



eggs. Numerous Lamellicorn and Heteromerous insects, 

 the latter remarkable for their deeply sculptured bodies^ were 

 slowly crawling about ; while the Saurian tribe, the constant 

 inhabitants of a sandy soil, darted in every direction. Dur- 

 ing the first eleven days, whilst nature was dormant, the 

 mean temperature taken from observations made every two 

 hours on board the Beagle, was 51°; and in the middle of 

 the day the thermometer seldom ranged above 55°. On the 

 eleven succeeding days, in which all living things became so 

 animated, the mean was 58°, 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 sailed, in 

 the twenty-three days included between the 26th of July 

 and the 19th of August, the mean temperature from 276 

 observations was 58°.4 ; the mean hottest day being 65°.5, 

 and the coldest 46°. The lowest point to which the thermo- 

 meter fell was 41°.5, and occasionally in the middle of the 

 day it rose to 69° or 70°. Yet with this elevated tempera- 

 ture, almost every beetle, several genera of spiders, snails, 

 and land shells, toads, and lizards were all lying torpid be- 

 neath stones. But we have seen that at Bahia Blanca, 

 which is four degrees to the 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 orders of 

 animated beings. This shows how nicely the required degree of 

 stimulus is adapted to the general climate of the place, and 

 how little it depends on absolute temperature. It is well 

 known that within the tropics, the hybernation, or more pro- 

 perly estivation, of animals is governed by the times of 

 drought. Near Rio de Janeiro, I was at first surprised to 

 observe, that, a few days after some little depressions had 

 been changed into pools of water by the rain, they were 

 peopled by numerous full-grown shells and beetles. Hum- 

 boldt has related the strange accident of a hovel having been 

 erected over a spot, where a young crocodile lay buried in 



