BEGINNINGS OF THE NEXT -GENERATION'' 101 



transformation of frog life. Of this 120, three J -lived^ long 

 enough to become real frogs, while one hundred and seven- 

 teen died by accident or because 

 they could not get the right sort 

 of food after their legs appeared. 



The oldest of the three lived 

 three months. He had all four legs, 

 and everything was complete about 

 him except that his tadpole tail did 

 not fully disappear. Then he too 

 died. But the surprise was that 

 any lived at all. 



A record of this kind startles 

 every biologist, because nothing of 

 the sort is found anywhere in the 

 ordinary history of vertebrates. 

 What we learn from biological 

 history is that every descendant of 

 every vertebrate begins its indi- 

 vidual existence by the union of 

 two germ cells, each of which is 

 derived from a separate individual 

 of different sex. We learn that 

 unless this union takes place there 

 can by no possibility be a second 

 generation. 



Aside from vertebrates, however, 

 there are other living creatures to 

 whom this law of two starting cells 

 does not apply. The amoeba, for example, shows quite another 

 method. Here we have a one-celled creature that multi- 

 plies by pulling itself in two. To-day each amoeba that lives 



TADPOLE No. 2 



This also grew from an unferti- 

 lized egg that had been pricked 

 with a platinum needle. It died 

 after six months with rudimen- 

 tary legs only. (Courtesy of 

 Professor Loeb) 



