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Updated: May 24, 2025
Agassiz insists that ancient animals resemble to a certain extent the embryos of recent animals of the same classes; or that the geological succession of extinct forms is in some degree parallel to the embryological development of recent forms. I must follow Pictet and Huxley in thinking that the truth of this doctrine is very far from proved.
If it should hereafter be proved that ancient animals resemble to a certain extent the embryos of more recent animals of the same class, the fact will be intelligible. The succession of the same types of structure within the same areas during the later geological periods ceases to be mysterious, and is simply explained by inheritance.
The occurrence of gill-slits in the embryos of lizards, birds, and mammals now seems a small thing when compared with the correspondences disclosed by the earliest stages of development.
Until becoming acquainted with these facts, I was unwilling to believe in the frequent early death of hybrid embryos; for hybrids, when once born, are generally healthy and long-lived, as we see in the case of the common mule.
If this be true, and if in its development a flounder must review its mode of evolution as a species, the young fish ought to be symmetrical; and it actually is. The grotesque skate and hammerhead shark were demonstrated to be derivatives of a simpler type of shark; their embryos are practically indistinguishable from those of ordinary dogfish and sharks.
"Embryos and idiots, eremites and friars, A violent cross wind from either coast Blew them transverse. Then might ye see Cowls, hoods, and habits, with their wearers, tost, And flutter'd into rags; their reliques, beads, Indulgences, dispenses, pardons, bulls, The sport of winds." The mire was fully stirred up in which the hierarchy had enjoyed its sleep and sunshine for a thousand years.
These five primitive cerebral vesicles, that are found in the embryos of all the higher vertebrates from the fishes to man, and grow into very complex structures, remain at a very rudimentary stage in the Cyclostoma. The histological structure of the nerves is also less advanced than in the rest of the vertebrates.
If it should hereafter be proved that ancient animals resemble to a certain extent the embryos of more recent animals of the same class, the fact will be intelligible. The succession of the same types of structure within the same areas during the later geological periods ceases to be mysterious, and is simply explained by inheritance.
During the whole of this time there are no embryos in the uteri, and therefore it might be urged absorption of hormones from the embryos cannot be the cause of the persistence of corpora lutea in pregnancy. But it seems to me that a complete answer to this objection is supplied by the peculiar relations of the embryos to the pouch in Dasyurus and other Marsupials.
Hence the coco-nut in its unstripped state is roughly triangular in form, its angles answering to the separate three fruits of simpler palms; and it has three pits or weak places in the shell, through which the embryos of the three original kernels used to force their way out.
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