Nov. 27, 1873] 



NA TURE 



THE COMMON FROG* 



V. 



'T'HE third order of the class Balrachia is made up of 

 -I a few creatures the distribution of which is limited to 

 the warmer regions of the earth, where one of the genera 

 (Ccnilid) comprising the group is distributed over both 

 hemispheres, being found in India, Africa, and South 

 America. Two other genera {Sipkoiwps and Rltina- 

 ircina) are exclusively American, while a fourth genus 



[Epicriinii] is only found in Asia. The order is called 

 OpJtioniorplia. These creatures are singularly unlike the 

 frog in external appearance, as they are entirely destitute 

 of limbs and have quite the appearance of earthworms, 

 because they are not only very long and slender, but have 

 also a skin which is soft and naked. By earlier naturalists, 

 and even by Cuvier, they were classed with snakes. 



In spite of this striking dissimilarity between the 

 Ophioinorpha and ^l/toiird, the former are really more 

 like frogs than they are like efts in one important respect. 



FlG. ■2i.—C<rdlia. 



This is because, for all their elongated figure, the tail in 

 them is quite rudimentary or altogether absent. 



Tlic Ophioinoipha would by many be supposed to 

 present an analogy with serpents, from their long and 

 elongated bodies, and from the utter absence of limbs. 



There are, however, but very few snakes (the " rough- 

 tails '' L ■ropeltidir and the Toiiria'da) which have long 

 bodies and very short tails. 



It is rather the singular family of lizards, AmphishcnidcB 

 (with one exception completely limbless) that the Ophio- 

 morpha resemble. 



increases their resemblance to earth-worms) and feed on 

 worms and other small animals and mould. 



To turn now to another aspect of our subject, let us 

 consider the relations of the Frog to past time. If, ex- 

 tending our survey over the records of past epochs, we 

 search the tertiary and all other rocks above the Lias for 

 fossil allies of our Frog, we shall (judging by what we yet 

 know) fail to find any not at once referable to one or 

 other of the three ordinal groups above enumerated. 



Fossil frogs and toads have as yet only been found 

 down to the miocene, the oldest being some found in the 

 so-called ''brown coal' wliich is imt a carboniferous deposit 



These Amphisbenians have a softer skin than any other 

 ;Saurians except chameleons. It is also marked in 

 grooves which are arranged in transverse rings. They 

 have an exceedingly short tail which is blunt, so that, the 

 head being small, one end of the body is as large as the 

 other. 



The Ophioinoipha also have the body marked with 

 numerous transverse grooves or rings ; they are utterly 

 devoid of limbs, and the head is scarcely, if at all, larger 

 than the hinder end of the body. 



These creatures burrow beneath the soil (which habit 



* Continued from p. 30. 



at all. The remarkable thing, however, is that the differ- 

 ence between these oldest known Frogs and the existing 

 forms is so very trifling. They are as complete and 

 thorough frogs as any that live now. 



Agam, the fossil Urodeles similarly resemble their ex- 

 isting representatives, and no one extinct species exhibits 

 characters in any way tending to bridge over the chasm 

 which separates the Urodcia from the Anoura. 



When, however, we descend to the Lias, Trias, and 

 Carboniferous rocks, we come upon a rich variety of 

 extinct species of animals evidently allied to those forming 

 the three Batrachian classes already described. They form, 

 however, an order by themselves, to which the term Laby- 

 rinthodonta has been applied, and thus our search into 

 I the past has brought us a rich and important harvest, 



