406 CHARLES DARWIN 



so methodically along well-chosen tracks. Near the springs 

 it was a curious spectacle to behold many of these huge 

 creatures, one set eagerly travelling onwards with out- 

 stretched necks, and another set returning, after having 

 drunk their fill. When the tortoise arrives at the spring, 

 quite regardless of any spectator, he buries his head in the 

 water above his eyes, and greedily swallows great mouthfuls, 

 at the rate of about ten in a minute. The inhabitants say 

 each animal stays three or four days in the neighbourhood 

 of the water, and then returns to the lower country; but 

 they differed respecting the frequency of these visits. The 

 animal probably regulates them according to the nature of 

 the food on which it has lived. It is, however, certain, that 

 tortoises can subsist even on these islands where there is no 

 other water than what falls during a few rainy days in the 

 year. 



I believe it is well ascertained, that the bladder of the frog 

 acts as a reservoir for the moisture necessary to its exist- 

 ence : such seems to be the case with the tortoise. For some 

 time after a visit to the springs, their urinary bladders are 

 distended with fluid, which is said gradually to decrease in 

 volume, and to become less pure. The inhabitants, when 

 walking in the lower district, and overcome with thirst, often 

 take advantage of this circumstance, and drink the contents 

 of the bladder if full : in one I saw killed, the fluid was quite 

 limpid, and had only a very slightly bitter taste. The inhabit- 

 ants, however, always first drink the water in the pericar- 

 dium, which is described as being best. 



The tortoises, when purposely moving towards any point, 

 travel by night and day, and arrive at their journey's end 

 much sooner than would be expected. The inhabitants, from 

 observing marked individuals, consider that they travel a 

 distance of about eight miles in two or three days. One large 

 tortoise, which I watched, walked at the rate of sixty yards 

 in ten minutes, that is 360 yards in the hour, or four miles a 

 day, allowing a little time for it to eat on the road. During 

 the breeding season, when the male and female are together, 

 the male utters a hoarse roar or bellowing, which, it is said, 

 can be heard at the distance of more than a hundred yards. 

 The female never uses her voice, and the male only at these 



