  The study of their morphological coherence allows us to obtain a better
understanding of the morphological evolution of open clusters. We employed the
ellipsoid fitting method to delineate the 3D spatial structure of the sample
clusters while using the morphological dislocation (MD) defined in our previous
work and the ellipticity ratio (ER) of the clusters' inner and outer structures
to characterize the morphological coherence of the sample clusters. The results
show an inverse correlation between the ER of the sample clusters and the
number of their members, indicating that sample clusters with a much more
elliptical external morphology than internal shape generally tend to host a
large number of members. Meanwhile, a slight shrinking of the MD of the sample
clusters with their members' number may shed light on the significant role of
the gravitational binding of the sample clusters in maintaining their
morphological stability. Moreover, there are no correlations between the MD and
ER of the sample clusters and their age. They are also not significantly
correlated with the X-axis, the Y-axis, their orbital eccentricities, and the
radial and vertical forces on them. However, the ER of the sample clusters
displays some fluctuations in the distributions between it and the above
covariates, implying that the morphologies of the sample clusters are sensitive
to the external environment if sample effects are not taken into account.
Finally, the analysis of the 3D spatial shapes of sample clusters with a small
ER or a large ER demonstrates that the number of members lays an important
foundation for forming a dense internal system for sample clusters. At the same
time, the MD of the sample clusters can serve well as an indicator of their
morphological stability, which is built upon a certain amount of member stars.
