CROCODILES 55 



and Dakosaurus were quite defenceless, and these 

 are known to have been marine forms, and there- 

 fore removed from dangers of this kind. Noto- 

 suchus of the Cretaceous was also defenceless, and 

 apparently a swamp-dweller. The one or two 

 species of armoured marine crocodiles must be 

 regarded as originally river crocodiles which had 

 not had time to lose their armour before extinc- 

 tion overtook them. A form known as Teleo- 

 saurus, of the Lower Oolite, had dorsal and 

 ventral armour. 



Long descriptions of the internal organs would 

 be out of place here, but a few brief comments 

 on one or two which will serve to bring out the 

 differences between the Crocodiles and other 

 Reptiles should certainly be acceptable. 



The organs of sense are well developed. The 

 eyes, in addition to an upper and lower eyelid, 

 are provided with a peculiar sheet of membrane 

 which can be drawn across the eyeball. This is 

 known as the nictitating membrane, and is ex- 

 ceedingly thin and transparent. Its movements 

 carry over the eye a watery fluid secreted by a 

 special gland, and thus its surface is kept con- 

 stantly moistened. When under water this cur- 

 tain is drawn over the eye as a protection, its 

 transparency being so great as to leave vision 

 unimpaired. 



The position of the eyes and nostrils are 

 directly connected with the habits of the animal. 

 Both are placed on the top of the head, pro- 

 jecting considerably from the surface. This 

 arrangement allows the animal when in the 

 water to breathe and see at the same time whilst 



