لكن بالنوع بمعنى أنها لم تخل قط عن صورة
But by kind, meaning they have never lacked some form.
This describes an alleged uninterrupted succession of forms: one form disappears and another follows, with no absolute gap in the series. The claim is about the eternity of the succession rather than the persistence of one particular individual.
Merely observing that present things arose from earlier things is insufficient to prove this. Every observed case having a predecessor is one proposition; the entire series actually lacking a beginning is a further proposition requiring its own justification.