78 REPTILES AND BATRACHIANS 



arranged in transverse series, below. The tail, which is 

 always very long, is rounded in terrestrial and arboreal 

 species, compressed and sharp-edged above in those fre- 

 quenting the water ; in these it is made use of as a weapon 

 of defence, the lizards lashing out vigorously with this 

 organ at their enemies. In conformity with the semi- 

 aquatic life of many of them, the nasal opening leads into 

 a cavity situated on the snout, the aperture closing and 

 retaining a certain quantity of air, thus enabling the lizard 

 to remain for a considerable time under water. The 

 parietal, eye-like organ, alluded to in the chapter on 

 Sphenodon, is less degenerate in the Monitors than in any 

 other lizards. 



With the exception of the Land Monitor, V. griseus, 

 all these creatures are good cHmbers, ascending to the top 

 of trees to plunder the nests of birds. This land Monitor, 

 a comparatively small species, inhabiting North Africa and 

 South- West Asia, seldom exceeding four feet in length, is 

 greyish-yellow in colour, harmonizing with the sand of the 

 desert in which it lives. 



The Nile Monitor, F. niloticus, and the White- 

 throated Monitor, V. albigularis, are two African species ; 

 the former is found all over the continent with the excep- 

 tion of the north-western part, while the latter is confined 

 to South and South-Eastern Africa. The Nile Monitor 

 is very abundant on the banks of the Upper Nile, where it 

 searches for the eggs and young of crocodiles, and is there- 

 fore, although much feared by the natives, regarded with 

 the very greatest respect. The general colour is dark 

 brown, or black above, with yellow spots on the back and 

 limbs. In the young the yellow markings are ocellar and 



