PAET II. THE LOWEE YEBTEBBATA. 



CHAPTER XIII. THE FROG. 



1. External Form and Mode of Life. The common 

 frog (Eana temporaries) has many obvious differences from 

 the rabbit. Instead of a land-loving animal, running and 

 burrowing, eating vegetable food, we have now a creature 

 equally at home on land or in fresh water, leaping and 

 swimming, and living almost exclusively on insects. Its 

 skin is devoid of hair and nails, and so abundantly beset 

 with glands as to be always moist. It is richly coloured, 

 and possesses in some degree the property of varying in 

 colour in accordance with its surroundings. The ajbauce 

 of a neck is characteristic of aquatic vertebrates, since a 

 gradual passage from head to trunk offers the most suitable 

 form for swimming (see chap, i., 2). The absence of a 

 tail is more surprising, since it is the organ of swimming, 

 noiTonly in fishes, but in newts. The frog, however, has 

 greatly developed hind legs which replace a tail in function, 

 while on land they enable it to progress by sudden leaps 

 instead of the swift crawling which really constitutes the 

 motion of a newt. The disadvantage (on land) of the neck- 

 less condition is no doubt compensated for by the remarkable 

 way in which the eyes project up beyond the general 

 surface of the head, instead of being deep-sunk in a bone- 

 protected orbit, as are the rabbit's. There is no external 

 ear^in the frog, the tympanic membrane being flush with 

 the general surface, and easily recognized as a circular 

 patch of the skin behind the eye. The mouth-opening is 

 huge, extending literally from ear to ear, since there are no 

 cheeks or lips. The external nares occupy much the same 

 position as in the rabbit. Posteriorly, instead of separate 

 anus and urinogenital opening we have a common cloaca! 



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