INTRODUCTION 



relationship, than did the many resemblances which 

 have been long recognised as existing between them. 

 The second part thus proves what the first part onl}' 

 rendered probable. 



In such an investigation as this a writer is always 

 open to the charge of having interpreted the facts as 

 he wished to interpret them. I cannot of course den}- 

 that the speculation was of such absorbing interest 

 that I was not indifferent to the conclusion, and that I 

 therefore naturally seized upon the facts most favour- 

 able for the establishment of my argument ; but at 

 the same time I am not conscious of having ignored 

 difficulties. If, nevertheless, I have unconsciously 

 distorted the facts in order to establish my con- 

 clusions, I comfort myself by the reflection that those 

 conclusions are of such great zoological importance 

 that they cannot long pass unchallenged. 



I may perhaps mention the fact that whereas in the 

 first part I have relied almost entirely upon my own 

 researches into the anatomy of the Apodidse and of 

 the carnivorous Annelids, in the second part I have 

 had to draw many of the facts used in the arguments 

 from the works of others. 



My sincere thanks are due to Professor Ernst 



