VARIATION AND ADAPTATION 223 



water, while in forms that practise an amplexus, such as Triton 

 waltlii, T. asper, etc., there is no crest. On the hypothesis of 

 the inheritance of acquired characters this difference is ex- 

 plicable, the crest of the male being attributed to the effect of 

 the pressure of the water in the active vibratory movements which 

 the male continues for hours or days in presence of the female. 



In the Anura the hind limbs are elongated in adaptation 

 for jumping as in many other animals, such as the kangaroo, 

 the grasshopper, and the flea. The segments of the legs are 

 all elongated, including the tarsus (ankle) and the attachment 

 of the pelvic girdle to the vertebral column is shifted far for- 

 wards so that the number of presacral vertebrae — the vertebrae 

 in front of the sacrum — is reduced to nine or less. The effect 

 of this is to place the application of the force of propulsion near 

 to the middle of the body and so give greater efficiency. The 

 hind toes are usually united by a web or membrane for the 

 purpose of swimming in the water, the frog swimming with its 

 hind feet, while the newt swims with its tail. In some cases 

 the toes of the fore-foot are also webbed, but this seems not to 

 be an adaptation for swimming, as in the most completely 

 aquatic species such as the Aglossa Pipa and Xenopus the front 

 toes are free, and the webbed condition of these toes occurs in 

 arboreal species. In Nectophryne, a genus of the Bufonidae 

 occurring in Africa, India and the East Indies, the toes of both 

 fore and hind limbs are webbed, and the species of this genus 

 are believed to be arboreal, while in the allied species Nectes 

 subasper of Java the fore toes are free and the animal is aquatic. 

 Perhaps the webbing of the fore toes is always adapted for sup- 

 porting the animal in the air during its leaps in the trees, as in 

 RhacopJiorus pardalis and other species of the same genus. 

 R.pardalis was first described by A. R. Wallace in his Malay 

 Archipelago. It was brought to him by a Chinese workman 

 who said he saw it come down in a slanting direction from a 

 high tree as if it flew. The feet are not only fully webbed, 

 but much enlarged, so as to present a greater surface; this 

 species lives in the forests of Borneo and the Philippine Is- 

 lands ; its total length is two and a half inches. 



In the arboreal Anura the ends of the toes are expanded 

 into adhesive discs by which the animal is able to attach itself 

 firmly to the surfaces of leaves. It is a well-known fact that if 



