. Evolution and its relation to religious thought . B. Fig. 61.—Vertebrated but symmetrical fin, a, form ; b, structure. ]Sow, in the development of a teleost fish (Fig. 58),as has been shown by Alexander Agassiz,* the tail-fin isfirst like Fig. 61; then becomes heterocercal, like Fig. 60;and, finally, becomes homocercal like Fig. 59. Why so ?Not because there is any special advantage in this succes-sion of forms ; for the changes take place either in theQgg or else in very early embryonic states. The an-swer is found in the fact that tliis is the order of change * Proceedings of American Acad
. Evolution and its relation to religious thought . B. Fig. 61.—Vertebrated but symmetrical fin, a, form ; b, structure. ]Sow, in the development of a teleost fish (Fig. 58),as has been shown by Alexander Agassiz,* the tail-fin isfirst like Fig. 61; then becomes heterocercal, like Fig. 60;and, finally, becomes homocercal like Fig. 59. Why so ?Not because there is any special advantage in this succes-sion of forms ; for the changes take place either in theQgg or else in very early embryonic states. The an-swer is found in the fact that tliis is the order of change * Proceedings of American Academy of Arts and Sciences, , May, 1878. 156 EYIDEXCES OF THE TRUTH OF EVOLUTION. in the pliylogenic series. The earliest fish-tails wereeither like Fig. 61 or Fig. 60 ; never like Fig. 59. Theearliest of all were almost certainly like Fig. 61; thenthey became like Fig. 60 ; and, finally, only much later ingeological history (Jurassic or Cretaceous), they becamelike Fig. 59. This order of change is still retained inthe embryonic development of
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