AFFINITIES OF BOAS 
also harmless and green snakes, which frequent trees. 
Snakes are divisible into a considerable series of families. 
The most important of these are the Boide, the Colu- 
bride and the Viperide. The Boide are, as the names 
suggests, the Boa constrictor and its allies, the pythons, 
anaconda, and the European and Old World genus, 
Evyx, besides some less known forms. 
The greatest interest attaching to these snakes is that 
they stand at the base of the Ophidian series ; they have 
not so completely lost the characteristics of the more 
lizard-like form from which snakes, as we think, must 
have been derived. For they possess what no snakes, 
except certain immediate allies of their own, belonging 
however to other families, possess, distinct rudiments of 
the hind limbs, which are even visible externally, as a 
small claw on either side of the vent. They have also 
two lungs, whereas in the more modified snakes the lungs 
have dwindled down to a single one and, at the most, a 
tiny rudiment of the other. This reduction of the lungs 
is also seen in the limbless lizards, but it is not so fully 
carried out in all of them as it is in the modified vipers 
among snakes. Otherwise the pythons and boas are 
typical snakes to all outward appearance, and have no 
essential peculiarities externally, which mark them off as 
something distinct from other snakes, save only the 
hooks already mentioned. Allied to the Boide are 
several families of small and burrowing snakes, such as 
the Typhlopide, Ilysiide, and Uropeltide, of which 
representatives are not, as a rule, to be seen at the Zool- 
ogical Gardens. 
The Colubridz, or Colubrine snakes embrace the vast 
majority of species of the snake tribe, and the family 
includes some of the most deadly of theirkind. People 
used to group together the venomous as opposed to the 
non-venomous serpents ; but it is now seen that this 
physiological attribute is not sufficient to outweigh real 
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