1972] 
Hlavac — Prothorax of Coleoptera 
47 
terior collar completion. Either a medial sternal projection or lateral 
edges of the cryptosternum is/are joined to notal projections, e.g., 
figs. 42, 43 vs. 50, 51. The presence of similar collars, differing in 
minor details, in numerous groups of beetles reflects a broad selec- 
tion pressure acting through a narrow gap-like pathway. And, of 
course the probability of multiple origin, and convergent improve- 
ment is quite high in this and other structural integrity improving 
adaptations. 
Variability of structures increasing prothoracic power generation 
is limited by the geometry of muscle origins and insertions. Sev- 
eral distinct pathways are possible. For example, figs. 27, 42, 47 
depict a trio of high volume prothoraces with three different, spe- 
cialized pleuro-coxal mechanisms (as compared with that of con- 
figurations differing slightly from the generalized reference standard, 
figs. 25, 32, 37). In two cases, the endopleuron is fused to the 
notal wall, but two different strategies of coxal reaction to notal 
increase have been employed (figs. 27, 44). In figs. 45, 47, deep 
coxal internalization is also employed but the pleuro-coxal mech- 
anism is completely different. The pleuron is reduced and attached 
to the coxa; both rotate about a notal condyle. In each of these 
cases, a specialized pleuro-coxal mechanism is uniform throughout a 
large, biologically diverse higher taxon — i.e., superfamily. And each 
type of mechanism is present in, at least, several unrelated taxa. 
The observed diversity of internal mechanics in high volume forms 
is consistent with a relatively specific selection pressures having acted 
through a broad, multi-solution pathway, followed by canalization. 
The prothoraces of some surface dwelling forms are simply low 
in volume and have the same pleuro-coxal mechanism as do substrate 
inhabitants of the same taxon, e.g., Adephaga, Scarabaeoidea (figs. 
45, 47). On the other hand, the design limitations of a flexing pro- 
coxa have resulted in similar configurations in the several groups of 
surface grade beasts that have adopted this locomotory mode (figs. 
30, 35, 40). 
Prothoracic structure is then sensitive to changes in locomotory 
biology in but a limited number of ways. And, the broad adaptive 
radiations of Coleoptera may be documented through the study of 
prothoracic morphology. But since adaptive pathways are so narrow, 
convergence so common, and putatively unique paradaptive features 
so infrequent, only limited evolutionary conclusions can be drawn 
solely from prothorax morphology. The obvious historical questions 
on ecological differentiation of individual higher taxa circumscribe 
a major poorly explored area of beetle systematics. Useful ideas on 
