he chick (fig. 8) and of man (fig. 9) possess at an early
stage in their development gill-slits on the sides of the neck like those
of fishes. No one familiar with the relations of the parts will for a
moment doubt that the gill slits of these embryos and of the fish represent
the same structures. When we look further into the matter we find that
young fish also possess gill slits (fig. 10 and 11)--even in young stages
in their development. Is it not then more probable that the mammal and bird
possess this stage in their development simply because it has never been
lost? Is not this a more reasonable view than to suppose that the gill
slits of the embryos of the higher forms represent the adult gill slits of
the fish that in some mysterious way have been pushed back into the embryo
of the bird?

[Illustration: FIG. 11. Side views of head of embryo sharks, showing gill
slits.]

I could give many similar examples. All can be interpreted as embryonic
survivals rather than as phyletic contractions. Not one of them calls for
the latter interpretation.

The study of the cleavage pattern of the segmenting egg furnishes the most
convincing evidence that a different explanation from the one stated in the
biogenetic law is the more probable explanation.

[Illustration: FIG. 12. Cleavage stages of four types of eggs, showing the
origin of the mesenchyme cells (stippled) and mesoderm cells (darker); a,
Planarian; b, Annelid (Podarke); c, Mollusc (Crepidula), d, Mollusc
(Unio).]

It has been found that the cleavage pattern has the same general
arrangement in the early stages of flat worms, annelids and molluscs (fig.
12). 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.

Accepting this view, let us ask, does the evidence from embryology favor
the theory of evolution? I think that it does very strongly. The embryos of
the mammal, bird, and lizard have gill slits today because gill slits were
present in the embryos of their ancestors. There is no other view that
explains so well their presence in the higher forms.

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 to