X INTRODUCTION. 



possession of rudiments of limbs nol visible externally. A few lizards 

 have the ears covered by the skin, and others have no eyelids. There are 

 serpents and lizards which have similar forms, motions, and habits. The 

 extent of variation may best be seen by comparison of the examples cited 

 below. 



Development of the senses varies according to habits. In the serpent- 

 tongued lizai-ds we meet with great quickness of sight, hearing, scent and 

 touch, accompanied by lack of taste — the tongue simply being a very sen- 

 sitive tactile organ. Again, in species living upon vegetation, the touch is 

 deficient and the tongue is short and thick, evidently an organ of taste. 

 The keen-sighted Chamaeleon has a tongue which is probably an organ 

 of taste as well as touch. 



Many of the Saurians are noted for transient variations of color. The 

 cause of these changes is found in the presence of pigments of different 

 coloi's at various depths below the surface of the skin. The expansion or 

 contraction of one or more of the layers, in consequence of muscular action, 

 nervous irritation, or contraction or inflation of the lungs, changes the pro- 

 portion of the different pigments visible at a particular instant. If the 

 upper layer contains the dark pigment, the contraction of its chromato- 

 phores lessens the visible amount of this color and exposes a greater amount 

 of that beneath it. These changes arc not to be confounded with that occur- 

 ring on soils of light color, or in regions where there is great reflection of 

 the rays of light; in such localities permanent lightening of the colors is 

 apparently due to a bleaching process undergone by the pigments. It seems 

 as if the effect of polarized light upon the pigment differed from that of the 

 direct unpolarized rays. Commonly each vertebra is concave in front and 

 convex behind. To this there is a very marked exception in the case of the 

 Uii yxchocephalia, a suborder founded on a family represented by a single 

 genus of New Zealand lizard, Hatteria or Sphenodon. Externally this ani- 

 mal resembles the species of the European genus Lacerta so much that one 

 can hardly believe it more than generically distinct. Skeletal structure and 

 details of anatomy discover differences of sufficient importance to warrant 

 the establishment of a different order. .Most noticeable of its peculiarities 

 are the series of palatine teeth, the structure of the skull, the biconcave 

 vertebrae, the presence of a cartilaginous rib beneath each transverse fold 

 of the skin of the abdomen, and the absence on the male of intromittent 

 sexual organs. Of those examined the females were lighter in color, and 



