38 THE STORY OF REPTILE LIFE. 



an instance where lie and his five companions, 

 when thus suffering, found relief by killing one 

 of the species known as Testudo vicinia, a native 

 of Albemarle Island. They found no less than 

 five cups of clear fluid in this receptacle. Simi- 

 larly Darwin relates in his "Voyage of the 

 Beagle " how that the contents of the bladder 

 are also, under pressure, greedily drunk. The 

 taste of the fluid is said to be bitter, whilst that 

 of the pericardium is tasteless. 



The difference between the fresh- water or pond 

 Tortoises and Terrapins and their cousins of the 

 dry land are generally by no means such as would 

 strike one at first sight. So closely do they 

 resemble one another, indeed, that some surprise 

 might naturally be expressed that such different 

 environments should have effected so little change. 

 The only difference between the land and aquatic 

 forms appears to be in the form of the feet, the 

 aquatic species having webbed feet, which may 

 even become paddle-shaped. A more careful 

 examination of one of these pond-tortoises would, 

 however, reveal modifications which are obviously 

 special adaptations to their peculiar mode of life. 

 Besides the change in the form of the feet to 

 facilitate movement through the water, special 

 breathing organs have been developed to permit 

 of prolonged submersion. Thus in certain " soft- 

 shelled " tortoises of the sub-order Trionychoidea, 

 the mucous membrane of the throat is beset with 

 thread-like processes richly supplied with blood. 

 These act like the gills of fishes, fresh water 

 being constantly taken in through the mouth 

 and passed over the delicate blood-filled pro- 



