CONCLUSIONS 155 



It seems at times as if many of our modern writers on evolution 

 have had their views by some sort of revelation and they base 

 their opinions on the evolution of life, from the simplest form to 

 the complex, entirely on the nature of specific and intra-specific 

 evolution. It is possible that this type of evolution can explain 

 many of the present-day phenomena, but it is possible and indeed 

 probable that many as yet unknown systems remain to be dis- 

 covered and it is premature, not to say arrogant, on our part 

 if we make any dogmatic assertion as to the mode of evolution 

 of the major branches of the animal kingdom. 



Perhaps it is appropriate here to quote a remark made by 

 D'Arcy Thompson in his book On Growth and Form. " If a tiny 

 foraminiferan shell, a Lagena for instance, be found living today, 

 and a shell indistinguishable from it to the eye be found fossil in 

 the Chalk or some still more remote geological formation, the 

 assumption is deemed legitimate that the species has ' survived ' 

 and has handed down its minute specific character or characters 

 from generation to generation unchanged for untold millions of 

 years. If the ancient forms be like rather than identical with 

 the recent, we still assume an unbroken descent, accompanied by 

 hereditary transmission of common characters and progressive 

 variations. And if two identical forms be discovered at the 

 ends of the earth, still (with slight reservation on the score of 

 possible ' homoplasy ') we build a hypothesis on this fact of 

 identity, taking it for granted that the two appertain to a common 

 stock, whose dispersal in space must somehow be accounted for, 

 its route traced, its epoch determined and its causes discussed or 

 discovered. In short, the Naturalist admits no exception to the 

 rule that a natural classification can only be a genealogical one, 

 nor ever doubts that ' the fact that we are able to classify organ- 

 isms at all in accordance with the structural characteristics which 

 they present is due to their being related by descent.' " 



What alternative system can we use if we are not to assume 

 that all animals can be arranged in a genealogical manner? The 

 alternative is to indicate that there are many gaps and failures 

 in our present system and that we must realise their existence. 

 It may be distressing for some readers to discover that so much 

 in zoology is open to doubt, but this in effect indicates the vast 

 amount of work that remains to be done. In many courses the 



