THE EVOLUTION OF ANIMAL FUNCTION 327 



vestigate the behaviour of organisms or of their parts, under 

 conditions to which they are not normally subjected, is to 

 burden biology with so much useless fact. The question was 

 fought out recently over Roux's programme for the study 

 of experimental embryology. The clearest possible answer has 

 been given to all who sought to oppose the artificial method, 

 by those fundamental facts which the school of experimental 

 embryology has already contributed to the understanding of 

 embryological development. Indeed, as far as I am aware, no 

 sound argument has ever been adduced why biology should be 

 condemned to struggle along without making every possible use 

 of that abstraction from special conditions which is the very 

 essence of the experimental method. Biology surely, beyond 

 all other sciences, finds the phenomena which she has to 

 investigate entangled in special conditions. The organism 

 presents to every cell a most limited routine, and only by 

 breaking through that routine shall we begin to disentangle the 

 essential properties of the cells from their chance associations. 



If, then, the general problem is stated, and the essential 

 method of observation is determined, we have yet to decide at 

 which end of evolutionary history investigation should begin. 

 Are we to learn first to know the properties of the unicellular 

 animal, and then to trace these as they diverge and become 

 isolated in the specialised cells of the higher organisms ? Or 

 is the method to be the reverse of this ? This question will 

 certainly be answered in practice by one consideration only — at 

 which end it is easier to begin. On this matter it has been 

 urged by Verworn that cell-physiology should begin with the 

 unicellular organism. The reasons given for this decision 

 are, in the main, the statement that every cell, even the most 

 physiologically specialised, has to perform all the elementary 

 functions of life, and the fact that physiological specialisation 

 brings with it morphological complexity. As to the first of 

 these reasons, one need only recall that the nerve fibre is freed 

 from the duty of ingesting solid food particles, and from the 

 performance of contractile changes, to realise that physiological 

 specialisation does actually carry with it the suppression of 

 some elementary vital phenomena. The question of morpho- 

 logical complexity is beside the point when the object of study 

 is not form but function. I venture to think that when the 

 investigation of any function is in hand the first object of 



