320 BULLETIN 34, UNITED STATES NATIONAL MUSEUM. 



HYLIDJE.* 



VertebrcB procoelons. Sacral diapopliyses dilated, the simple urostyle 

 articulated to two condyles. External raetacarpi bound together. Ter- 

 minal phalanges articulated iuferiorly onto the extremity of the penulti- 

 mate, globular or swollen proximally, and giving rise, usually from a cen- 

 tral emargination, to the curved, acute distal portion, which is of a more 

 compact tissue. Superior plate of ethmoid never covered by fronto- 

 parietals, usually produced anteriorly between frontonasals. Ear per- 

 fectly developed. Abdominal integument generally areolate. 



This family embraces the tree toads of Australia and America. It 

 presents comparatively little structural variety, not containing as un- 

 developed types as the Cystignathidie, nor as high ones; it possesses 

 neither earless nor fossorial, nor really aquatic genera. 



The adaptive modifications are: First, those which accompany a ter- 

 restrial habitat, ie., the diminution of the digital dilatations and palma- 

 tion. These occur in regularly increasing degree in a small number of 

 the species of the typical genus Hyla, and are general in and distinctive 

 of two other genera. Second, those which adapt the extremities to 

 grasping a limb by opposition of digits, instead of adhering to a snr- 

 face by expansion of them in one plane. This first appears possible in 

 Agalychnis, and is structural in Phyllomcdusa. Third, those which re- 

 strict the light admitted to the retina, first, by the lateral contractility of 

 the pupil; second, by the rendering opaque of the inferior palpebra. The 

 first characterizes the two genera just mentioned, the last occurs in the 

 first two, but is inconstant in the second, and characterizes two other 

 genera. Fourth, that which adapts the female duiiug the breeding sea- 

 son to localities without water, or where perhaps the water contains 

 enemies, by the inversion of the dorsal integument so as to form a sack, 

 in which the eggs are carried. This occurs in and is accepted as char- 

 acteristic of two genera. 



Another feature, which has a functional value, is the union of the 

 abdominal integuments with the 6ui)erficial fascia of the muscles by 

 an areolar or fibrous net- work, continuous with that of the usual latero- 

 ventral band. The skin of the inferior surfaces of these creatures, as in 

 the raniform tree frogs, has a thickening in numerous close areohB, the 

 nature and function of which is like that of the digital dilatations, and 

 the derm of the tuber on the thumb of the male liana, i. e., to secrete an 

 adhesive fluiLl as aid in maintaining the peculiar positions assumed. 

 In proportion to the development of these is the extent of the abdomi- 

 nal attachment, and hence may be supposed to be adapted for relieving 

 the other areolar connections from the strain of the animal's weight when 

 in an appressed or vertical position. Its uniformity in the burrowing 

 genera of the Bufonidte and Scaphiopodidie, and especially on their dor- 

 sal surface, rather confirms this view. 



This connection is, hoMCver, evidentlj^ not necessary to the use of the 



opiates 72, 73, 



