uncertainty even now of the construction of the theory of descent. As soon as we go into details it leaves us in the lurch; it was only while our knowledge was small that everything seemed to fit together in most beautiful order.” (Quoted by Dwight in “Thoughts of a Catholic Anatomist,” p. 187.) It is undeniable, indeed, that in many cases the young of higher animals pass through stages in which they bear at least a superficial resemblance to adult stages in inferior and less complex organisms. Obviously, however, there cannot be any direct derivation of the _embryonic_ features of one organism from the _adult_ characters of another organism. This preposterous implication of the Müller-Haeckel Law must, as Morgan points out, be entirely eliminated, before it can merit serious consideration. Referring to the spiral cleavage exhibited by annelid, planarian and molluscan eggs, Morgan says: “It has been found that the cleavage pattern has the same general arrangement in the early stages of flat worms, annelids and molluscs. Obviously these stages have never been adult ancestors, and obviously if their resemblance has any meaning at all, it is that each group has retained the same general plan of cleavage possessed by their common ancestor.... Perhaps someone will say, ‘Well! is not this all that we have contended for! Have you not reached the old conclusion in a roundabout way?’ I think not. To my mind there is a wide difference between the old statement that the higher animals living today have the original adult stages telescoped into their embryos, and the statement that the resemblance between certain characters in the embryos of higher animals and corresponding stages in the embryos of lower animals is most plausibly explained by the assumption that they have descended from the same ancestors, and that their common structures are embryonic survivals.” (_Op. cit._, pp. 22, 23.)