22 



REPORT — 1855. 



It will here be seen that it is thought preferable to abide by the older 

 classification, which considers the Amphipoda and Isopoda as distinct orders 

 of the second division, than as separate groups of the same order as classified 

 by Dana; in this, we think, we are justified upon strictly anatomical reason- 

 ing, for there appears to be as great, if not a more distinct separation, between 

 the Amphipoda and the Isopoda, than between the Amphipoda and the 

 higher types of Crustacea. 



This latter opinion is one on which Dana is again opposed to Edwards and 

 the older naturalists *. 



The former considers the Isopoda a higher type of Crustacea than the 

 Amphipoda, whereas Leach, Latreille, Desmarest, Lamarck, and Edwards 

 have each respectively placed them next, succeeding the Stomapoda in the 

 descending scale. 



This difference of opinion involves and necessarily opens the question of 

 the homological relation of parts between the different orders or groups of 

 Crustacea, the discussion of which will enable us, we hope, to see how much 

 or little the same organs resemble each other when adapted to forms higher 

 or lower in the scale ; and their closeness or dissimilarity will enable us to 

 approximate toward a tolerably correct estimate of the value of the unity of 

 typical development, and thereby judge the relation which one form of Crus- 

 tacea may hold to another. 



The older European naturalists, and Edwards in particular, consider the 

 Edriophthalma as formed upon the same general type as the Podophthalma ; 

 not so the American carcinologist, who affirms that " they have not a 

 macroural characteristic, but have a body divided into as many segments as 

 there are legs (whence our name Choristopoda) ; the antenna, legs and whole 

 internal structure are distinct in type." — Vol. i. p. 1404'. 



The consideration of the structure of the Amphipoda is one that has little 

 attracted the attention of either naturalists or physiologists. This remark 

 is the more correct in relation to our own country, where, we are not aware 

 that there has yet been published a single communication on the internal 

 organization of this order, except a short paper on the CaprellcB, by Mr. 

 H. Goodsir, in the Edinburgh Philosophical Journal for July 1842. 



The labours of Montagu were mostly directed to the pursuit of objects, 

 and the important addition of figuring and describing the outward appear- 

 ances of his results. The attention of Leach was confined to describing, 

 generalising and classifying all known species, whether the result of his 

 own discoveries or that of others. The researches of most later writers have 

 been extended to the elucidation of local faunas only. Dr. Thomson of 

 Belfast read at the British Association, and published in the Annals of 

 Natural History for 1847, a series of papers on the Crustacea of Ireland. 

 Dr. Johnston of Berwick has during an industrious career (alas ! too early 



* Mihie-Edwards. 



Legio (II.) Edriophthalma. 

 Ordo I. Amphipoda. 



„ II. Isopoda. 



„ III. Laemodipoda. 



Order T. Amphipoda. 



Family. I Family. 



Gammaridse. I Hyperidae. 



Tribus. Tribus. 



Sauteurs.Marcheurs. Gammaroides. Anormales. 

 Ordiuaires. 



Dana. 

 Subclassis II. Edriophthalma. 

 Ordo I. Choristopoda. 

 Tribus 1 . Isopoda. 



„ 2. Anisopoda. * 



„ 3. Amphipoda. 



Tribus 3. 



Amphipoda. 



Families. 



Caprellidea. Gammaridea. Hyperidea, 



