479 
Flight, or the power of moving through the air for some 
considerable distance, has been acquired by animals in different 
classes, such as fishes, lizards, birds, and mammals. In the case 
of birds and bats, although the details differ, yet the conversion 
of the front limbs into organs of flight have been paralleled. 
Nearly all the examples cited above are functional homo- 
plasmy, or adaptations of certain organs for certain uses, and it 
is of great interest to note that the great majority of the most 
conspicuous cases of homoplasmy are of that nature, for it 
shows very forcibly the direct or indirect influence of the environ- 
ment upon the organism. 
3ut there are innumerable cases of homoplasmy in which it 
is difficult to connect any functional use. Such are well known 
to any systematist who has worked at a large group and has 
attempted to draw conclusions as to their relationship. Every 
entomologist could cite innumerable examples, so I will only 
refer to a few of those which I find in the group which I have 
paid most attention to, and recently published upon, namely, the 
fulgorid Homoptera. 
In fulgorids we find a vein in the fore-wing, which is gener- 
ally considered as the costa. In many forms, including what I 
consider to be the most primitive, we find this vein coincident 
with the costal margin, but in others it is some distance from 
the margin and thus forms a precostal cell or “costal area” 
which is often crossed by a number of veins. This condition has 
arisen at least twice among the fulgorids and most likely several 
times. The amalgamation of the basal portion of the veins has 
taken place many times quite independently, even within a single 
family ; the commonest is the amalgamation of the subcosta and 
radius, but the radius and media have also amalgamated to- 
gether; and also the subcosta, radius, and media. The clavus is 
normally closed, but in more than one family (i. e., Derbidae, 
Flatidae, and Fulgoridae) it is found to be open in some genera. 
Among the Flatidae there are some genera in which the claval 
veins do not form a fork, a condition peculiar to the Cicadoidea. 
The arrangements of the branching of the veins and the condi- 
tions of the cross-veins are paralleled many times in the super- 
family. The reduction of wings in the superfamily has taken 
place many times quite independently. Another character used 
