S4: ON THE PHYSIOGNOMY OF SERPENTS. 
law, that the younger the individual the more vivid are the 
colours, and more distinct in their distribution ; and often 
the tints which adorn the young are effaced in the old, or 
they become absolutely uniform ; for instance, in the Colu- 
ber canus, C. melanurus, the Homalopsis buccata, the 
Xenodon severus, and others. 
The faculty of spontaneous change of tint, — a faculty 
which many Batrachians, a great number of Saurians, and 
particularly Cameleons, possess, — is only observed in an 
inferior degree among Ophidians, and that principally among 
the climbing serpents distinguished by their green colour. 
The differences which exist between the relative colours 
of the male and female, and the changes produced in either 
sex at the principal periods of life, have been little studied. 
Sometimes, as in the Tropidonotus Matrix, the two sexes 
perfectly resemble each other ; but this is not the case in 
the Common Viper, in which the markings of the female un- 
dergo successive changes before the individual attains the 
term of its full growth ; whilst the males on coming out of 
the egg, present tints analogous to those of the adult of the 
same sex. 
We have spoken above of the great influence exercised 
by the casting of the skin on the beauty of the original tints. 
The changes which it produces are so much more worthy 
the attention of the naturalist, that the moiilt operates by 
insensible degrees, and takes place several times in the 
year. 
It happens almost constantly that the tints of Ophidians 
are effaced in a great measure after death, or that, when ex- 
posed to the action of ardent spirits, they suffer changes 
more or less marked. The black, the brown, the ochre- 
yellow, and many other such colours, do not, however, al- 
ways lose even the lustre reflected by the uniform surface 
of the scales ; among the number of the species which re- 
tain their colours after death, are the Calamaria arctiventris, 
C. Brachyorrhos, the Tortrix maculata, the Xenopeltis, the 
Coronella rufula, the Lycodon Hebe, and L. subcinctus, 
the Coluber Constrictor, C..^sculapii, C. melanurus, several 
species of Naja, Homalopsis, Vipera, and a great many 
