Psyche 
[September 
136 
ones, are unable to crush, crack, or pierce cuticle but must attack 
through vulnerable membranous zones. Enclosing membrane hinders 
such forms. Of course, this argument applies to substrate dwelling 
forms as well. In addition, a substrate form not dependent on in- 
terstitial spaces must generate force against obstacles to make prog- 
ress. Consequently, features increasing structural integrity can be 
adaptations which prevent structural deformation as those locomotory 
forces are generated and also prevent membrane from coming in con- 
tact with abrasive materials. Increasing structural integrity can be 
a defense adaptation in either zone or a locomotory adaptation in a 
substrate zone. 
Extant members of the groups closest to the presumed ancestral 
stock of Coleoptera are surface dwellers, except possibly Merope 
(Mecoptera). The gross structure of fossil Lower Holometabola 
is similar to that of extant forms and suggests that these groups have 
been surface grade forms throughout their long history. 
Beetles are the dominant adult insects in substrate environments. 
Specialized coleopterous faunas occur in: leaf litter, soil, living, dy- 
ing and decomposing woody plants, dung, carrion, etc. In each hab- 
itat many members of at least several families are present. However, 
a diverse assortment of beetles is also found in the surface zone, par- 
ticularly on vegetative surfaces. 
The major diagnostic features of Coleoptera are adaptations for 
improved structural integrity. Beetles have entered and radiated in 
the substrate locomotory zone; and many higher taxa contain sur- 
face dwellers clearly derived from substrate grade forms. An increase 
in structural integrity can either be an adaptation for substrate loco- 
motion or for mechanical defense against predators. These facts and 
assumptions indicate that penetration of the substrate zone and de- 
velopment of these adaptations are related, and that both occurred 
rather early in the history of Coleoptera. Within the framework 
provided by Bock (1965), then, the following historical diagnosis 
is suggested. 
The suite of unique diagnostic characters of Coleoptera originated 
and/or became coordinated as a response to selection pressure for 
increased structural integrity encountered during initial entrance and 
radiation in a substrate locomotory zone. Individual characters, 
which may have originated on a surface zone as a. mechanical defense 
adaptation are preadapted for a change in zone and shift in function. 
The adaptive transformation of the coleopterous prothorax is but a 
part of the large scale reorganization of the locomotory system stim- 
ulated by a major change in ecology. 
