EXTERNAL FACTORS ON THE SPAWN DATE I5I 



(c) There has been exaggeration, and the omission of circumstances 

 that would help to explain what is claimed. 



{(l) Some occult cause, beyond our present understanding must be 

 invoked." 



If Fisher is right, then the incredulity may be due to a belief that 

 the story is intrinsically too improbable. This never occurred to me. 

 Frogs live their aquatic life invariably among algae, which dominate 

 the life of a pond. It has been said that if all the higher plants in a pond 

 were to be removed and replaced by glass models of the same shape 

 and size, the animal life in the pond would go on just the same. Re- 

 move the algae, and life would be vastly different. Knowing the 

 number of parallels between the behaviour of frogs and the behaviour 

 of algae, and that no two essential oils have the same chemical com- 

 position or the same smell, I have always thought the hypothesis 

 suifered from the difficulty of proof, rather than from any improba- 

 bihty. But there is no need to despair. After all, it was only in late 

 1957 that we had experimental proof that satellites were kept in their 

 orbits by gravitation. Up till then the whole thing had been a hypo- 

 thesis, based on a number of parallels ! 



Other Species 



I have not made any allusion to work on other species. So far as I 

 know, there are no statistically satisfactory analyses, but only a large 

 number of opinions. Even if figures are quoted, the authors commonly 

 omit to record the negative cases as well as the positives. Unless both 

 are recorded in such a way that either the authors themselves or their 

 readers can fill up all the four spaces in a 2 X 2 contingency table of 

 the type used freely in this book or iise some other statistical test, then 

 we cannot judge whether the statements are sense or nonsense. The 

 author may be right, but all we can do is to accept or reject what he 

 thinks, and this is not science. If, however, we do choose to rely on the 

 author's good judgment, then I should say that there is plenty of 

 evidence that some species are affected by rain, but that temperature 

 correlations are doubtful. 



The British Herpetological Society is collecting data on all British 

 species and in time these should become valuable. The Secretary, at 

 the Zoological Society of London, will be glad to send report forms 

 to any interested person. 



