  We suggest the quasiparticle picture behind the integrable structure of N=2
SYM theory,which arises if the Lax operator is considered as a Hamiltonian for
the fermionic system. We compare the meaning of BPS states with the one coming
from the D-brane interpretation and give some evidence for the compositeness of
the selfdual strings. The temperature phase transition with the disappearance
of the mass gap is conjectured.
