Natural History of the United States. 247 



** degrees of organization," to designate orders. It is true 

 Lamarck uses the same expression to designate classes. We find, 

 therefore, here as everywhere, the same vagueness in the defini- 

 tion of the different kinds of groups adopted in our systems. 

 But if we would give up any arbitrary use of these terms, and 

 assign to them a definite scientific meaning, it seems to me most 

 natural, and in accordance with the practice of the most success- 

 ful investigators of the animal kingdom, to call orders such 

 divisions as are characterised by different degrees of complication 

 of their structure, within the limits of the classes. As such, I 

 would consider, for instance, the Actinoids and Halcyonoida ii> 

 the class of Polypi, as circumscribed by Dana ; the Hydroids, 

 the Discophorse, and the Ctenoids among Acalephs ; the Crinoids, 

 Asterioids, Echinoids, and Holothurise among Echinoderms; the 

 Bryozoa, Brachiopods, Tunicata, Lamellibranchiata among Ace- 

 phala ; the Branchifera and Pulmonata among Gasterpods ; the 

 Ophidians, the Saurians, and the Chelonians among Reptiles; the 

 Ichthyoids and the Auoura among Amphibians, etc." 



It would be injustice to the author not to state that in the suc- 

 ceeding paragraph he carefully guards the reader against suppos- 

 ing that he denies or ignores distinction of rank in other groups, 

 as in classes, for instance ; but he holds that here it is predomi- 

 nant. We could have wished that the view had been followed 

 farther into detail ; for, taking orders as we now have ihem, there 

 are some evident exceptions. In the birds, for instance, the orders 

 differ far more markedly in adaptation to conditions of life and 

 -structures depending on these, than in grade. In the orders of 

 insects there is the same idea, along with that of type or pattern 

 in a subordinate form ; for we must bear in mind that type, and 

 the homologies which express type, descend in different degrees 

 through all our sub-divisions from the great leading types to the 

 genera. It is expressed as distinctly in the elytia of beetles and 

 the scales of butterflies as in the skeletons of vertebrata or articu- 

 culata ; it is curious, too, that naturalists have differed so very 

 much as to the rank of the orders of insects. In other groups 

 again, as the reptiles, the idea of rank is quite patent in the orders, 

 but is much obscured when we add the fossil forms to those now 

 living. In the orders of Mammals, as lately proposed by Owen, 

 it is clearly exhibited. Dana has well shewn its existence in the 

 Crustacea. It is pretty evident also in the orders of the several 

 classes of Molluscs, and is very manifest in the Echinoderms. On 



