SECT. XV CLASSIFICATION OF CRUSTACEA 277 



This view explains the morphological significance 

 of the rostrum, as the protective point for the more or 

 less delicate antennae, arising, not per se^ but as the 

 further development of the tip of the middle piece 

 between the two depressions along which the antennae 

 travelled forwards. 



From all that remains then of these primitive 

 Nebalidae we see a sufficient resemblance to the 

 Apodidai to form a very striking confirmation of 

 our theory. We see in them true transition forms 

 between Apus and the higher Crustacea ; the fossils 

 showing very clearly one of the first steps in this 

 transformation, and one of the most needful for 

 success in the struggle for existence, i.e. the gradual 

 migration of the antennai to a frontal position near 

 the eyes. 



The many points of likeness between Apus and the 

 Macrura will already have struck every reader of the 

 first part of this book. The detailed deduction of 

 Astacus from Apus on the lines here laid down 

 would be a most interesting and profitable study. 



Starting, then, from our theory that Apus, owing 

 to its likeness to an Annelid, must be one of the racial 

 forms of the whole group, we have been able, with 

 varying success, to show that all ancient Crustaceans 

 are clearly related to Apus, and that all the chief 

 groups of the modern Crustacea, with the probable 

 exception of some of the Ostracoda, can be more or 

 less clearly deduced from Apus. An attempt to derive 

 the modern forms from the Apodidse in detail would 



