VI 



PREFACE 



one chapter, the first. This unduly large chapter is broken 

 up into sections which serve instead of the usual division of 

 so large a number of pages into chapters. The parts of the 

 Treatise on Zoology dealing with the Mollusca, the Arthropoda, 

 and the Vertebrata are in active preparation. 



E. RAY LANKESTER 

 May 15, 1903. 



