xvi 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 only 

 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 deny 

 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 Apodidae 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 



