PART II 



SECTION XII 



RELATION OF APUS TO THE OTHER CRUSTACEA 



Ix Part I. we have endeavoured, on morphological 

 and anatomical grounds, to deduce Apus from a car- 

 nivorous Annelid. We have shown that the trans- 

 formation of the latter into the former was in 

 adaptation to a new and very simple change in the 

 manner of life of the Annelid. If the reasoning of 

 Part I. is correct, we feel justified in concluding on 

 the ground of probability that the transformation of 

 Annelids into Crustaceans only took place once, and 

 that therefore our bent carnivorous Annelid must form 

 the root of the whole Crustacean system. Further, it 

 is clear that the Apodidae must stand very close to 

 this root. This reasoning leads us at once to find an 

 infallible test for our whole theory. We have two 

 lines along which to work, both of which are capable 

 of leading to a positive answer, negative or affirma- 

 tive. We shall first take the archaic forms and see 

 whether they, like Apus, are capable of being deduced 



