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 
