DEVELOPMENT OF THE COMMON FROG. 123 



limb is always forced through the gill-opening, the margin 

 of which is torn in consequence of the size of the natural 

 aperture being too small to allow its passage. On the 

 right side the opening is usually a ragged rent in the skin, 

 which has become thin at that part. The effect of the 

 protrusion of the fore legs is at once to stop aquatic respi- 

 ration and throw all the work of breathing on the lungs : 

 the animal remains almost constantly on the surface ; and 

 it very soon becomes exhausted and drowns if it cannot 

 support its nostrils above water. 



The tail now rapidly shrinks, being absorbed and used 

 as stored-up nutriment by the animal during the time 

 when it is unable to feed. It remains several days in the 

 water in this state ; but when the tail has been reduced to 

 a brown stump about half an inch long, and the ali- 

 mentary apparatus is completed and fit for its approaching 

 new mode of life, the animal shows an instinctive desire to 

 climb. Reaching the border of the pond, it will make its 

 way up a steep or even perpendicular surface to the height 

 of several feet, if this be necessary in order to reach the 

 bank. Here, among the grass, numbers of them may be 

 seen leaping about, still with a stump of tail, which serves 

 as provision for several days longer, after which, when it 

 has entirely disappeared, the young frog has gained suffi- 

 cient experience to take small insects as food. 



In this life-history of the tadpole of the common frog, 

 the dates, given with the observations and drawings, have 

 been made use of to mark the number of days included in 

 each period; but no special value is intended to be set 

 upon the exact length assigned to each ; for, in strictness, 

 the dates refer only to the particular tadpoles examined. 

 They are true, however, for this one instance ; and they may 

 be of use for rendering more clear the proper order of suc- 

 cession of the different developments. Tadpoles hatched 



k2 



