76 MEANING OF ORDERS. 



Winged Insect transiently represents a structural 

 character that is permanent in the lowest order 

 of its class, that its second stage of growth tran- 

 siently represents a structural character that is 

 permanent in the second order of its class, and 

 that only in the last stage of its existence does 

 the Winged Insect attain its complete and perfect 

 condition, we may fairly infer that this division 

 of the class of Insects into a gradation of orders, 

 placing Centipedes lowest, Spiders next, and 

 Winged Insects highest, is true to Nature. 



This is not the only instance in which the em- 

 bryological evidence confirms perfectly the ana- 

 tomical evidence on which orders have been dis- 

 tinguished, and I believe that Embryology will 

 give us the true standard by which to test the 

 accuracy of our ordinal groups. In the class of 

 Crustacea, for instance, the Crabs have been 

 placed above the Lobsters by some naturalists, in 

 consequence of certain anatomical features ; but 

 there may easily be a difference of individual 

 opinion as to the relative value of these features. 

 When we find, however, that the Crab, while un- 

 dergoing its changes in the egg, passes through 

 a stage in which it resembles the Lobster much 

 more than it does its own adult condition, we 

 cannot doubt that its earlier state is its lower one, 

 and that the organization of the Lobster is not as 

 high in the class of Crustacea as that of the 



