Let us assert :
Preformation and epigenesis are equivalent : identities in terms of the Principle of Equivalent : Identity q.v.
For the common genesis of further growth in both is equivalent : identical
For the germ layers for instance and the sperm – the single individual sperm – as the genesis of a grown up adult (or at least grown up child, after passing as through all the forms of embryology) are equivalent : identical in form and structure
To be equivalent : identical in form and structure : [A] the smallest part from which the greater will grow will consist of a shape and motion similar to the grown up part - as in sperm [B] this matter : energy as in [A] is divisible that is formed of smaller parts that constitute the whole whether these parts be germ layers or otherwise in any way - as is manifest in both sperm and zygote and [C]
Both matter : energy as per preformation and epigenesis have and manifest equally these three requisites in III above.
Therefore accordingly and in as direct proportion preformation and epigenesis are equivalent : identical in terms of III above and therefore as equivalent : identical in terms of the Principle of Equivalent : Identity q.v.