THE HYDROPHIDiE AND THE AMPHISB^NID^. 141 



difScult, on a cursory glance, to distinguish the head 

 from the tail ; hence they have been called double-walkers 

 by the French, and double-headed snakes by some Eng- 

 lish writers : the eyes, like most of the slow-worms, 

 are so very small as sometimes to appear wanting ; the 

 vent is within an inch of the tail, and exhibits a row of 

 pores; while the whole body, excepting the head, which 

 is plaited, is encircled, in the typical species, with circu- 

 lar rows of quadrangular scales ; the teeth are small, 

 conical, and placed in the jaws ; while the second lobe 

 of the lungs, which in many of the true slow- worms is 

 reduced to a rudiment, becomes, in these reptiles, alto- 

 gether obsolete. The Amphisbcenidce are few in num- 

 ber, completely terrestrial, and are mostly found in the 

 warm latitudes of South America. 



(143.) The family of the Anguinidj^, or slow-worms, 

 completes the aberrant division of the serpents, and cor- 

 responds to the Ophidosaurij or lizard-serpents, of some 

 writers. Like all osculant groups employed by nature 

 to connect two very distinct tribes of animals, and 

 where, in consequence, there are very numerous modifi- 

 cations of form, it is exceedingly difficult to characterise 

 the AxGuiNiDiE by determinate characters : they may, 

 however, be considered in external appearance as very 

 much resembling a Julis or Millipede, so common in 

 decayed wood. The body is cylindrical, and perfectly 

 resembles that of the Amphishcenidce ; but, instead of 

 having quadrangular plates, they are covered by imbri- 

 cated scales, under which, upon dissection, are discovered 

 the bones of the shoulder and pelvis ; in the sub-genus 

 Pseudopus this affinity to the seps-lizards is carried so 

 far, that on each side of the vent there is a small protu- 

 berance, furnished with a little bone analogous to the 

 femur, and belonging to a true pelvis concealed under 

 the skin. The well-known slow or blind-worm of Eu- 

 rope is probably the type of this family ; and if we look 

 for the disappearance of all these vestiges of the lizard 

 structure, we find them in the slow- worms of America. 

 The truthj however, is, that the doctrine of types depends 



