sub species aeternitatis

Spinoza uses this phrase extensively, and I find
it translated and interpreted in a variety of ways.
Apparently "species" is the acc. plural of the
5th declension.  (I believe that, strictly speaking,
there is no acc. pl for "species", but that Spinoza
means the acc. pl anyway in his usages)
That means that "sub" should
only have the meanings which syntactically
call for the accusative case.  That should be a clue
in figuring out which of the many, many meanings
of "species" Spinoza meant to be using.

A straight forward translation would be

     "under the forms of Eternity"

but, altho that is correct in terms of the Latin
per se, I don't really like it in terms of the rest
of what Spinoza seems to be up to.  I am
inclined more toward those meanings which
are cognate to "aspect", "looking", etc.

So....

    does anyone have something to say as to
    what Spinoza meant with his uses of the
    phrase "sub species aeternitatis"?