GENERA OF THE ARCIFEROUS ANURA. b9 



with this succession, we have four modifications of this structure to adapt to as many 

 modes of life : the aquatic, the terrestrial, the arboreal, and the subterranean. As 

 the earth's surface is the common medium between the above extremes, so the 

 species of terrestrial habits furnish us with none of the adaptive extremes of struc- 

 ture, but remain an intermediate group, from which the succession of structures, 

 interrupted, it is true, passes towards the divergent types. Developemental 

 structures accompany and confirm the adaptive, but by no means coincide ; more- 

 over, the adaptive is the evanescent character, while the developmental is the 

 definitive. 



The aquatic habit is attained when the digits behind are not only webbed, but 

 when the external metatarsi are separated by membrane also. The arboreal, when 

 the terminal phalanges are furnished with a terminal transverse limb, which sup- 

 ports an adhesive disc. The subterranean is shortened, and furnished with a great 

 development of the first cuneiform bone of the tarsus, which is covered by a 

 corneous sheath, and serves as a spade. The first may be combined with the third, 

 as in Mixophyes and Chiroleptes, or it may be furnished with a bony over-roofing of 

 the temporal muscles, and penetration of its integuments by the ossification of the 

 cranium. 



The fossorial spur is weak in Helioporus, weaker in Platyplectrum, and just repre- 

 sented in Ceratophrys and Gomphobates. The palmate foot is diminished in Calypto- 

 cephalus, reduced in Mixophyes and Chiroleptes, and represented by a trace in 

 Hylorhina and Limnomedusa. The undeveloped ear is seen on one side only in a 

 species of Crinia, and in Alsodes. 



With regard to the dermal attachments, the following important varieties occur ; 

 in the family generally, but especially among Hylodes and Cystignathi, the dorso- 

 lateral septum is placed especially high up : — 



PSEUDES. — Septa in Pseudis as in Rana ; in Lysapus the lateroventral line is a 

 little widened. In JMixophyes fasciolatus the lateroventrals are very wide, 

 and leave the ventral free space very narrow behind the middle. 



Ceratophrtdes. — In (Gomphobates and) Tomopterna the lateral septa are narrow, 

 and there are two posterior abdominal transverse septa, similar to those attached to 

 the sternum. In Ceratophrys o r n a t u s these are wanting, but the dorsolateral line 

 is very broad. » 



Crinia. — Among these animals I have examined species of Helioporus, Platyplec- 



23 



