  This paper reports statistically significant correlations between various
burst parameters, observed in a sample of 156 GRBs belonging to BATSE 4B
catalog with T90 less than 2 s. The number of subpulses in a burst is strongly
correlated not only with the object's duration but also with its fluence and
hardness ratio, suggesting that when the central engine is more powerful,
ejecting matter with typically higher values of Lorentz factor, the bulk energy
is dissipated on longer time scales in the form of larger number of gamma
pulses. We estimate hard-to-soft lag in bursts by taking the difference between
centroids corresponding to time profiles at energies $> 100$ keV and $<100$
keV. The number of short GRBs that show soft-to-hard spectral evolution is
slightly over one quarter of the total, in the sample considered here. Bursts
that exhibit hard-to-soft spectral change appear to form a distinct class, with
strength as well as hardness of individual subpeaks tending to decrease with
peak position. Opposite is true for objects with softer photons arriving
earlier than the harder ones, implying some kind of a rejuvenation of the
central engine (may be due to enhanced accretion of matter towards the end).
The two classes also show other diverging trends. For instance, objects
belonging to the larger of the two classes display strong correlations between
spectral lag and the fluence, the hardness ratio as well as the number of
pulse, respectively. While no such correlations are seen in bursts that evolve
from soft to hard. However, the magnitude of lag is strongly correlated with
burst duration in both the classes.
