ON THE BRITISH EDRIOPHXHALMA. 1^ 



Crustacea. It therefore would embrace a large number of Crustacea, which 

 vary considerably in their habits and forms, some of them belonging to well- 

 organized beings, whereas others degenerate in character and descend to 

 those which assume an insect-like appearance. 



The first step therefore separated the Entomostracans ; and now when we 

 speak of the Edriophthalma, it is understood to be a legion intermediate 

 between Podophthalma and the JEntomostraca of recent Crustacea. But 

 this term still conveys too wide a signification. Latreille therefore divided 

 it into two, one of which he named Amphipoda, the other Isopoda. A third 

 subdivision was established by the same author, that of Ltsmipoda (or 

 LcBmodipoda*). This embraces an aberrant group of Amphipoda, which 

 previously were ranked among the Isopoda, and must be looked upon as 

 differing from the normal type in the rudimentary character of certain 

 parts, rather than as possessing separate qualifications of their own, warrant- 

 ing their being formed into an order of equal importance to the other two, 

 although it has been retained in this position by the profound authority of 

 Professor Milne-Edwards. 



Lamarck embraced these, together with the Amphipoda and Isopoda, as in 

 one family. 



Dumeril, in his ' Zoologie Analytique,' united the Amphipoda with the 

 Stomapoda, notwithstanding the pedunculated character of the eyes of the 

 latter, because in each of these genera the head, he thought, was " separated 

 from the corselet." To these united tribes he gave the name of " Arthroce- 

 phaUs " or " Capites." 



Desmarest, in his ' Considerations gen6rales des Crustaces,' has adopted 

 the order of Lcemodipoda which Leach united with the Isopoda, because he 

 thought the vesicular sacs to be " spurious " legs. 



M. Blainville, in classifying Crustacea, arranged these three under the 

 term Tetradecapoda, as antagonistic to that of Decapoda, whicl;i is synony- 

 mous with Podophthalma. The adaptation of the name by Blainville to the 

 sessile-eyed Crustacea, arose from the circumstance of their possession of 

 fourteen legs, but this characteristic circumstance is not a constant fact. 



It is true, that in Caprella the legs are obsolete, and in Anceus are altered 

 in form, though present; yet if these facts be not admitted of importance in 

 consequence of their homological signification, then we must include them 

 with the higher orders, for the only separation which naturally exists is the 

 modification of the forms of certain parts homologically the same. Thus it 

 will be found that ten-legged Crustacea exist among the sessile-eyed form, 

 which in all other respects are nearer allied to true Isopodes. Anceus and 

 Paniza, though only possessing ten perambulatory legs, approximate nearer in 

 their structural signification to the fourteen-legged Crustacea than to that 

 class, which the number of these legs would seem to suggest. 



The term Choristopoda, from ywpiarus separate, irovs foot, has been lately 

 applied by Mr. Dana, and is made synonymous by its author with the Tetra- 

 decapoda of Blainville, and includes the Amphipoda, Lcemodipoda, Isopoda 

 of authors, and the Anisopoda of Dana. 



Perceiving no advantage in the new term over its older synonym, and 

 fearing the result of multiplying names, it is the intention in this Report to 

 adhere to the one most commonly used, and on that account most generally 

 understood. We consider the second division of Crustacea as ^'rfno- 

 phthalma, using it as synonymous with Tetradecapoda of Blainville and 

 Choristopoda of Dana. 



* At first Latreille placed the animals belonging to this order among the Isopoda, section 

 Cystibranches. — (Dictionnaire d'Histoire Naturelle.) 



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