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 Boidae, the Colu- 

 bridae and the Viperidae. The Boidae are, as the names 

 suggests, the Boa constrictor and its allies, the pythons, 

 anaconda, and the European and Old World genus, 

 Eryx, 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 Boidae are 

 several families of small and burrowing snakes, such as 

 the Typhlopidae, Ilysiidae, and Uropeltidae, of which 

 representatives are not, as a rule, to be seen at the Zool- 

 ogical Gardens. 



The Colubridae, or Colubrine snakes embrace the vast 

 majority of species of the snake tribe, and the family 

 includes some of the most deadly of their kind. 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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