130 BULLETIN 160, UNITED STATES NATIONAL MUSEUM 



that have been adapted to an arboreal life. The ends of the fingers 

 and toes are provided with adhesive disks, by means of which these 

 tree frogs are able to obtain a firm foothold on relatively smooth 

 surfaces, though they are employed mainly for climbing and for 

 clinging to foliage and limbs when jumping. Diverse ecological niches 

 are filled mth different kinds of animals, and it is therefore not sur- 

 prising that Mexico with its varied climate and topography should 

 be endowed with a remarkable assemblage of hylids. Not less than 

 7 genera and 20 species are recognized in this review. 



Most peculiar of all these hylids is the marsupial frog Gastrotheca, 

 in which the whole brood is sheltered in a common pouch on the back 

 of the female. Another interesting genus, Phyllomedusa, is repre- 

 sented herein by three species. Some tree frogs of the genus Phyllo- 

 medusa are known to lay their eggs in nests of froth attached to leaves, 

 but unfortunately the life histories of those that occur in Mexico are 

 unknown, and it is barely possible that all of them may not have 

 acquired this curious habit. The eggs of one species of the diminutive 

 toothless Hylella are laid in the sheathing leaf bases of a dust-feeding 

 plant that grows on tropical trees. 



A curious adaptation to the habit of digging occurs in the genus 

 Pternohyla, which differs from other hylids in having a shovellike 

 internal metatarsal tubercle. Tree frogs without a visible covering of 

 skin on their heads also occur in Mexico. Besides Gastrotheca and 

 Pternohyla, there are two other little-known genera, Diaglena and Tri- 

 prion, with bony casques. The presence of palatine or parasphenoid 

 teeth in Diaglena and their absence in Triprion are quite inexplicable. 



The gradation in the size of the adhesive disks possessed by the 

 Mexican hylas suggests that arboreal adaptation has not progressed 

 with equal rapidity and that some species of the genus Hyla are better 

 adapted for climbing than others. The hind limbs of most of these 

 hylas are elongated for leaping, though the ability to jump seems to 

 vary with the different species. One of the larger species, H. venulosa, 

 has been known to leap and alight without injury from a height of 

 140 feet. The extent of the webbing between the toes varies in the 

 different species. In H. mioiympanum the toes are four-fifths webbed. 

 Some individuals of H. eximia have the toes not more than half 

 webbed. 



Within certain limits tree frogs can change their general coloration 

 so that their bodies will blend more perfectly with the surroundings. 

 These changes in color are more marked in some species than in others. 

 One of the most widely distributed Mexican species, H. baudinii, 

 seems to have an exceptional color range. Most of the Mexican hylas 

 have their own distinctive color patterns or markings and, while the 

 general coloration is not necessarily dull, brilliant hues are never 

 contiguous. 



