COLORATION 39 



Melanism is frequent in snakes, and sometimes 

 affects all individuals in the same locality. It 

 seems undesirable to bestow varietal names on such 

 aberrations, as is so frequently done by systematists, 

 any more than we should in the case of albinos. 

 Melanism may be produced in two ways : by an 

 extension of the black markings, which invade the 

 whole surface, as in the males of Vipera bents; or by 

 a general darkening of the ground colour and of the 

 markings, as in the females of the same species. In 

 the latter case, the markings reappear under certain 

 lights or after a prolonged sojourn in spirits. Some- 

 times, as in Zamenis gemonensis, the uniform black 

 colour appears only as the snake approaches the 

 adult condition, the young having the normal 

 livery. 



Partial albinism is rare; perfect albinism, charac- 

 terized by absence of black pigment in the eye, rarer 

 still. Cases have been observed, among European 

 species, in Tropidonotiis natrix and tessellatus, in 

 Coluber longissimus, and in Coronella austriaca. 



