INTRODUCTION 



of the Trilobites, I hesitated to discuss their relation 

 to Apus, and my knowledge of the Crustacea was 

 not sufficient to justify my attempting to form a 

 genealogical tree of the whole class. I intended to 

 content myself with an endeavour to show that in 

 the Apodid^e the process and method of the trans- 

 formation of carnivorous Annelids into Crustacea 

 was still visible in almost every organ and system of 

 organs. The unavoidable conclusion from this would 

 be, that Apus must be — for some groups at least — 

 the original form. 



Here I thought to leave the matter to be followed 

 up by zoologists whose knowledge and experience of 

 the special groups were greater than my own. My 

 curiosity, however, was too great, and after the first 

 part of this manuscript was practically in its present 

 form, I decided to see, by a study of Limulus and 

 the Trilobites, whether Apus was to be looked upon 

 as the original form of the modern Crustacea only, or 

 whether it could pass for the original of the whole 

 class, including these archaic forms. This investiga- 

 tion led to the writing of the second part, which was 

 thus an afterthought — an afterthought which, how- 

 ever, gives to the book whatever value it possesses. 



