94 



BRITISH SERPENTS. 



with the size of the adder. " Its length is contained 

 in the total from 5J to 7f times in the males, 8 

 to 9| times in the females." ^ The tail in the males 

 is not so sharply defined from the body as in females, 

 the whole adder tapering to a point without showing 



distinctly where the 



tail begins. In females 



the tail is much more 



obviously an appendage, 



being sharply defined, 



not so thick, and coming 



more abruptly to a 



point. The extra thick- 

 ness of the male tail 



is due to the presence 



in the anterior portion 



of it of the reproduc- 



tory organs of that sex. 



A side view of the tails 



of the two sexes at once 



brings the differences in 

 the tails into prominence. Diagrammatically they 

 are shown above. 



Numhcr of shields. — The male tail being the longer, 

 it is to be expected that the sub-caudal shields in 

 that sex are more numerous than in the female. 

 " The number (counting each pair as one, and not 

 reckoning the terminal, conical, or spine-like shield) 



^ Boulenger, Zoologist, March 1892. 



Fig. 21.- Male 

 TxViL (3 in. ) 



Fig. 22. — Female 

 Tail (21 in.) 



