148 MARINE CROCODILES. [CH. Ill 



Coupled with this series of facts, which will be dealt 

 with immediately, there is the tenacity of life of reptiles to 

 be constantly borne in mind. The most familiar example 

 of a Lizard which is almost entirely marine is the remark- 

 able iguanoid Amblyrhynchus of the Galapagos. Not 

 only does this lizard take long swims out to sea but it can 

 evidently only be drowned with difficulty. Darwin made 

 the experiment of sinking one to the bottom for several 

 hours, at the conclusion of which it appeared to be 

 uninjured. It is even a question whether the animals 

 may not possibly be able to respire oxygen dissolved in 

 sea water ; at any rate it seems certain that some other 

 reptiles, e.g. certain tortoises, can. The pharynx of a few 

 species, for instance the water tortoise Aspidonectes, is 

 provided with filamentary appendages, apparently attached 

 to the remains of the gill arches, which are full of blood 

 vessels and which enable the creature to breathe ; at any 

 rate this tortoise has been kept under water for the space 

 of 10 hours. It is held that these vascular tufts are the 

 homologues of the gills of the Amphibia, and it is quite 

 conceivable that this capacity for breathing oxygen dis- 

 solved in water may have been inherited by other reptiles 

 besides the tortoises. 



Apart altogether from theories there are other reptiles 

 besides the Amblyrhynchus which can swim with impunity 

 in sea water and which do so on occasions. 



The crocodiles of the present epoch are entirely fresh 

 water in habit; but the majority of the extinct families 

 were on the contrary marine. From the ancient Belodon 

 downwards we meet with the remains of the crocodiles in 



