DISTRIBUTION OF ORGANISMS. 173 



more serpentiform, and the limbs diminishing away to mere 

 rudiments, that it is impossible to assign exact limits to the 

 various genera. We may even see in the perfect varanians a 

 preparation for this new form. In these animals, the bones 

 of the head have, in part, that looseness of structure and 

 adherence which is carried to so remarkable an extent in the 

 serpents, which, being obliged to take their prey entire, could 

 not otherwise swallow it. The varanians, too, move in a ser- 

 pentine manner, using their long tail to aid their progression, 

 and to enable them the better to leap upon their prey ; pecu- 

 liarities in which they greatly resemble the serpents. In the 

 last lacertilia, the ribs are increased in number, the two pairs 

 of limbs are removed farther and farther from each other, 

 and become small and weak ; in some species the anterior, 

 and in others the posterior pair, alone remain ; until at last 

 they are reduced to mere rudiments which do not appear 

 above the skin. The common slow- worm is an example of 

 a lacertilian in this state. At the same time, to suit the 

 necessities of a body considerably attenuated, one of the lungs 

 is gradually shrunk up, until at length, in the true serpent, 

 only a vestige of it remains. Such is the actual history of the 

 great serpent families reductions from the lacertilia, to suit 

 a life generally skulking and furtive ; and there could not 

 well be a more lively illustration of the doctrine of the trans- 

 formation of animals. It furnishes a strong proof of the 

 readiness of nature to go back as well as to go forward, 

 according as circumstances shall dictate. It shows how 

 futile is the objection to the development theory, from such 

 facts as the crocodile-like arrangement of teeth in the theco- 

 dont lizards, the fathers of this order ; an advance of grade 

 being a saltus which may give such a superiority to the 

 patriarchs of a series, while it depends on the accident of ex- 

 ternal conditions whether this is to be improved upon, main- 

 tained, or degraded. Many existing serpents are much larger 

 than any existing lacertilia, the parent family ; but it must 

 be remembered that the early lizards were of enormous bulk. 

 How perfectly does palaeontology harmonize with this view 

 of the genesis of the ophidia! no fossil serpent occurring 



