chapter i 



THE EGGS AND YOUNG TADPOLES 



This book is an account of the life of the frog, planned as a complete 

 circle: complete, that is to say, in the same sense as a mcgalithic stone 

 circle is complete. The circle comes round again to the starting-point, 

 but there are gaps in it. 



Before this plan can even be started, a decision has to be made: 

 which comes first, the frog or the egg? I have chosen to put the egg 

 first, so that this chapter begins with an account of the jelly envelopes 

 and the part that these play in the ecology of the animals. If anyone 

 wishes to know how these eggs are laid, he must turn to Chapter 9, for 

 surely this is the ''other end" of the circle. 



The Connexion between the Distribution Range and the 

 Properties of the Eggs 



The frog is an inhabitant of cold climates. Fig. i shows its distribu- 

 tion, and it can be seen that it ranges very far north, even beyond the 

 Arctic Circle. In the more southern parts of its range, it becomes an 

 inhabitant of the liigh mountains. In the Alps, for example, it may be 

 found not far below the permanent snow line, at altitudes of over 

 2,500 metres where the snow only clears for just long enough for the 

 tadpoles to complete their metamorphosis before wintry conditions 

 set in at the end of September. In the Pyrenees, Balcells (1956) has 

 described colonies of tliis species on the Spanish side, although this frog 

 does not occur in the parts of France adjacent to these mountains. 



It breeds very early in the year, often as soon as the ice has gone from 

 its ponds, and sometimes even when it has not all melted, so that frogs 

 may be seen breeding in one part of a pond that still has ice or snow in 

 another place. 



How low a temperature the eggs can stand does not seem to have 

 been determined, but Fischer-Sigwart (1897) says that eggs frozen 

 through can still develop, and Douglas (1948) states that the eggs can 

 withstand o°C for at least twelve hours, so that the thermal death point 

 must he below this temperature. But wherever the actual point may 

 He, it is clear that the habit of the adults in spawning at such an early 



