GENERA OF THE ARCIFEROUS ANURA. 83 



EYLIDJE. 



Vertebrai procoelian. Sacral diapopliyses dilated, the .simple coccyx articulated 

 to two condyles. External metacarpi bound together. Terminal phalanges articu- 

 lated inferiorly on to the extremity of the penultimate, globular or swollen prox- 

 imally, and giving rise, usually from a central emargination, to the curved, acute 

 distal jjortion which is of a more compact tissue. 0. frontoparietalia shortened 

 anteriorly, usually embracing a fontanelle. Superior plate of ethmoid never covered 

 by frontoparietals, usually produced anteriorly, between frontonasals. Ear perfectly 

 developed. Abdominal integument areolate. 



This ftimily embraces the tree-toads of Australia and America. It presents com- 

 paratively little structural variety, not containing as undeveloped types as the 

 Cystignathidte, nor as high ones : it possesses neither earless genera, nor fossorial, 

 nor really aquatic. 



The adaptive modifications are : first, those which accompany a terrestrial habitat, 

 i. e., the diminution of the digital dilatations and palmation. 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 surface by expansion of them in one plane. This first appears in a species of 

 Agalychnis, and is permanent in Pithecopus and Phyllomedusa. Third, those which 

 restrict 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 three genera just mentioned, the last occurs in the first two, but is 

 inconstant in the second, and ap2)ears in two species of the genus Hyla. Fourth, 

 that which adapts the female during the breeding season to localities without water, 

 or where perhaps the water contains enemies, by the inversion of the dorsal integu- 

 ment so as to form a sack, in which the eggs are carried. This occurs in, and is 

 accepted as characteristic of two genera, of one species each ^ but as it occurs in but 

 one sex its value is questionable. 



Another feature, which may have a functional value, is the union of the abdominal 

 integuments with the superficial 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 nume- 

 rous close areolae, the nature and function ot which is like that of the digital dilata- 

 tions, and the derm of the tuber on the thumb of the male Rana, /. e., to .secrete an 

 adhesive fluid as aid in maintaining tlie peculiar positions assumed. In proportion 

 to the developeraent of these, is the extent of the abdominal attachment, and hence 

 may be supposed to be adapted for relieving the other areolar connections from the 



