von Baer's laws

proper noun

Four rules to explain the observed pattern of embryonic development in different species: (i) The more general characters of a large group appear earlier in the embryo than the more special characters. (ii) From the most general forms the less general are developed, and so on, until finally the most special arises. (iii) Every embryo of a given animal form, instead of passing through the other forms, rather becomes separated from them. (iv) The embryo of a higher form never resembles any other form, but only its embryo.