X.J THE COMMON FROG, 149 



blood in their respectively appropriate channels. 

 Nevertheless, further examination has shown us that 

 this heart is provided with a special arrangement of 

 parts so delicately co-adjusted as to be able to act 

 thus as efficaciously as does the heart of animals 

 much higher in the scale. Respiration, too, we have 

 seen provided for partly by an effective throat air- 

 pump, partly by a peculiar activity of the cutaneous 

 structures. 



We have, moreover, found that this complex adult 

 condition is arrived at by means of a rapid metamor- 

 phosis from an immature condition wonderfully dif- 

 ferent, indeed, but no less perfectly adapted to the 

 life conditions of the tadpole state. 



It remains now "to sum up the results" of our 

 investigations through *' a series of wider and wider 

 comparisons " to answer, finally, as far as may be, the 

 initial question of this little treatise. 



We have, in the first place, seen that the frog be- 

 longs to an order far more distinct from cognate 

 ordinal groups than is man's order from other orders 

 of his class — mammalia. We have also seen that the 

 frog belongs to an order which is singularly homo- 

 geneous, and yet that the class which includes it is 

 remarkably heterogeneous. 



Again, we have found that the subordinate groups 

 of the frog's order, families and genera, have very 

 definite relations to space, and that the order, as a 

 whole, is, as far as yet known, remarkably restricted 

 as regards geological time. 



The comparisons instituted in our survey of the 

 frog's anatomy, will enable us now to sum up resem- 



