based on the principle of Cephalization.—Insects. 13 
or nervous system, have not been referred to among the above 
characteristics, because (1) they often undergo very wide varia- 
tions under a given type, and especially in its inferior or degra- 
dational subdivisifh ; further, (2) when any internal condition 
is distinctive of a natural group of species, there is always some 
type or plan of general structure corresponding to it in limits; 
and (3) the type or plan of structure is the surest criterion as to 
whether a group is natural or not. As an example of this last, 
ture distinct natural groups. Besides other decisive distinctions, 
the former have without exception prehensile fore-feet, while in 
the latter, these organs are defunctionated of this power of pre- 
-Aension, and are simply locomotive organs. 
CLASSIFICATION OF INSECTS. 
been shown to depend on a transfer of force and function away 
m the systemic centre; and this by an abrupt transition, pro- 
ducing an abrupt downward step in grade, ; ; 
_ This retroferent transfer is exhibited prominently in the wings, 
the anterior wings in the Metasthenics having little or no use in 
flying. These organs have been stated to have eminent import- 
ance in the order of Insects because the type is aérial. There is 
additional reason for this importance in the fact that the dorsal 
side of an animal is the superior, and the ventral, the inferior ; or, 
the former is the more central in the life-system, and the latter 
the os circumferential. inca o 
‘8 the series of legs, as well as wings, may p’ cases 
transfer of Leama sites Gees the terms Pacbens and Metas- 
enics become more precise if reference to the wings is included. 
They will thus be (ategoy being the Greek for wing) (1) Plero- 
, and (2) Ptero-metasthenics. The two-winged species 
