AUSTRALIAN SNAKES. 17 



svoiild be diflficult ; such aid is furnished by the tail. 

 This member is very short, often no longer than the 

 body is thick, and is provided with a horny, thorn-like 

 point directed downwards. On being pressed against 

 the ground, this thorn provides the necessary point of 

 resistance. 



Another modification of the same condition is to be 

 found in earth snakes from the Philippine Islands, in 

 which the tail terminates in a disc or sliield, its 

 truncated appearance suggesting that the snake had 

 been chopped in halves. 



Land snakes, as above-mentioned, have their lower 

 surfaces covered with large transverse plates instead of 

 scales, and it is the edges of these plates catching 

 against the inequalities of the ground which offer the 

 necessary resistance during progression. As sea snakes 

 move by means of the tail alone, abdominal plates are 

 not necessary, and are consequently absent, excepting in 

 one genus. These plates are replaced by scales, similar 

 to those found on other parts of the body, but different 

 from the scales of the land snakes. Instead of being 

 imbricate, or overlapping like slates on a roof, they are 

 usually laid side by side, and are smooth and highly 

 polished, thus offering the slightest possible resistance 

 to the progression of the snake. They are generally 

 six-sided and vary much in size ; sometimes they 

 are slightly keeled and, in certain genera, the imbrication 

 has not been entirely lost, for we must look upon the 



