INTRODUCTION xv 



The attempted proof in the first part that Apus is 

 an original Crustacean easily derivable from an 

 Annelid, however interesting in itself, must have 

 remained little more than a curious morphological 

 study. The appeal made in the second part to 

 palaeozoic Crustacea must, however, be decisive as to 

 whether our claims for Apus as one of the original 

 forms can be definitely established. 



In commencing Part II., it was no small encourage- 

 ment to find that most of the earlier zoologists, as if 

 by instinct, classed Apus with the Xiphosuridae and 

 the Trilobites. This provisional classification had 

 not, however, held its own, and it was necessary to 

 examine the reasons why it had not clone so, and to 

 see if it was not after all justified by the facts. My 

 investigations led me to the conclusion that if Apus is 

 deducible from a carnivorous Annelid in the manner 

 described in the first part, there is no possible escape 

 from accepting a similar derivation for the Giganto- 

 straca, as Haeckel has called these ancient forms. I 

 found that, strange as it may at first seem, the 

 very differences between Apus and these ancient 

 Crustaceans yielded almost more striking proofs of 

 their having had the same origin and of their close 



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