THE NATTERJACK. 139 



is nearly the same in effect, " when we consider 

 that there are two rows in the spawn of the 

 natterjack, while in the common toad there is 

 only one." As the calculation is based upon the 

 space occupied by a single ovum, whence the 

 number contained in so many cubic inches is cal- 

 culated, we cannot comprehend how that number 

 is influenced by the ova lying in pairs or singly. 

 Further, the observation that in one species the 

 line is single and in the other double arises 

 probably from regarding the alternate ova in the 

 one chain as a single zigzag line, and not as a 

 double chain with the ova alternately arranged. 



After adverting to the uses of the tadpoles in 

 the economy of nature, the same gentleman 

 inquires, " What becomes of these myriads of 

 tadpoles ? " and sets about to furnish an answer. 



Few of those vast swarms that blacken the waters in 

 spring with their dusky forms, ever reach the perfect frog. 

 Their enemies are many, their means of defence few. They 

 become the prey of larger or more warlike animals than 

 themselves. These constant attacks greatly thin their 

 numbers. Thus by the time they are fit to leave the water, 

 they are, though still somewhat numerous, much less so than 

 at an earlier period of their existence. But having left the 

 waters, they are still exposed to great dangers. They are 

 greedily devoured by the snake, weasel, polecat, and by 

 nearly every species of water-fowl. 



Amongst the creatures who feed largely upon 

 the toad and frog in its larval state, are enume- 



