THE APPENDICULATE PHYLUM 55 



possess stalked eyes and a carapace, agree in their 

 internal anatomy completely with the sessile-eyed, 

 carapaceless Amphipods and Isopods. It would seem, 

 therefore, that the latter owe their comparatively low 

 type of organization to a secondary simplification of 

 structure, and that the so-called higher Crustacea 

 preserve to a larger extent the primitive character of 

 the ancestral Malacostracan. The study ofAnaspides 

 supports this view, for whereas in many features it 

 offers a starting-point for the divergence of the two 

 groups, in other respects it possesses the organization 

 of the more highly organized Malacostraca. Without 

 going into details, it may be said that the general 

 lesson to be learnt from Anaspides is that the evidence 

 of its being of a primitive nature is found not in the 

 absence of structures characteristic of the more 

 modern and specialized groups, but in the possession 

 of features which have been retained or elaborated in 

 one of the higher groups and lost in the others. It 

 cannot be too much insisted on that the history of 

 evolution shows a balance-sheet in which, the better 

 it is known, the more nearly are the losses seen to 

 equalize the gains. 



Besides the large and important groups of the 

 Appendiculata which we have considered, there 

 are several smaller assemblages of animals which 

 have for long puzzled systematists but are probably 

 degenerate or simplified offshoots from the Annelid 



