8 Experimental Zoology 



but only because we have found that death always takes place 

 under ordinary conditions. Suppose, however, we change the 

 conditions ; might we not hope to prolong the duration of life ? 

 Improbable as this may seem, there are already experiments 

 afoot that indicate that, however difficult, the problems may 

 not be insoluble. 



Why, on an average, in most animals, are equal numbers of 

 two forms born male and female ? Is there an internal 

 mechanism? If so, what regulates it? Do external or inter- 

 nal conditions determine that one egg becomes male, another 

 female? Even if an internal mechanism exists, it might be 

 affected by external conditions, and in any case the cause of 

 the production of the two types must be determined. 



Observation has established that the evolution of animals and 

 plants has, in all probability, taken place. But what factors are 

 involved in the process are unknown. Only in ' the last few 

 years by means of an experimental study of the subject has 

 decided advance been made. 



It is sometimes stated that nature has already carried out 

 innumerable and wonderful experiments, and that we can 

 never hope to excel her in this power. Is it not better, therefore, 

 to examine patiently and reverently what she has done, and in 

 this way learn how her processes have been carried out? Let 

 us not be blinded by rhetorical questions of this kind. No 

 doubt nature has carried out prodigious experiments; but we 

 can never be certain that we know how she has obtained her re- 

 sults until we can repeat the process ourselves. What would 

 the chemist or the physicist say if he were told that nature has 

 already carried out experiments on a much greater scale than 

 he can hope to accomplish, and that he should drop his ex- 

 perimental methods and study his physics in a thunderstorm 

 and his chemistry in a volcanic eruption ! 



I have brought up this point because it illustrates one side 

 of the experimental method that is sometimes overlooked. Al- 

 most all of the phenomena with which the biologist has to deal 

 are so complex that he cannot determine what part each factor 



