XII INTRODUCTION. 
in two opposable groups. Such an arrangement of the toes, with the pre- 
hensile tail, enables the animals to walk lengthwise of the small branches 
with readiness. They spend their lives in the trees, and feed mainly upon 
insects, capturing them with the tongue, which can be thrust forward several 
inches for the purpose. The females lay from eight to a dozen eggs under 
the fallen leaves. In this group the transient variations of color are exces- 
sive in amount and rapidity; they often differ on opposite sides. Ability 
to take on at will the color of any object upon which an individual may be 
placed does not exist. 
Most of the Gecconide have rudimentary eyelids, and the eyeball covered 
by a transparent membrane under which it moves with freedom. <A few 
have connivent lids. The pupil is most often oblong and erect. The tongue 
is short and thick. The skin is covered with granular or tubercular promi- 
nences, Which are not imbricated. In the greater number of the species the 
feet are provided with adhesive apparatus under the toes in the shape of 
expansions or transverse series of plates, with which they are able to cling 
to vertical and smooth surfaces. These disks vary greatly in the different 
genera. Sometimes there are no disks, and sometimes the claws are absent. 
Occasionally the claws are retractile as in cats. The body and head are 
commonly depressed. When broken or lost, the tail grows out again; it 
may be reproduced a number of times in the life of the individual. This 
organ takes on fantastic shapes in some species; in all it is very fragile. 
Ptychozoon is marked by fringed dermal expansions on sides of tail, body, 
and head, which form a sort of parachute, answering a similar purpose 
when leaping to that of the membranes of Draco. The name Gecco is given 
in imitation of the voice. Geccoes live in the tropics of both hemispheres. 
Some frequent houses, where they are very useful on account of their insec- 
tivorous habits. In the United States a single species is represented, 
Sphacriodactylus notatus Bd., at Key West, Florida. Three or four others, 
belonging to Coleonye, Diplodactylus and Phyllodactylus, are reported from 
Sonora and Lower California. Farther South they are more common. 
The Agamide belong to the Eastern Hemisphere. In this family the 
eye and eyelid are well developed, the teeth are generally planted upon the 
upper edges of the bones of the jaws, the tongue is thick, and slightly, or 
not at all, extensile, the scales are imbricate, and the tail not nearly so 
fragile as in other Saurians. The toes are without disks. Of the odd forms 
in the various subfamilies, probably none is more striking than that of the 
