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Feb. 1846

22

Reflecting on Falconers' case of series of Mastodons & Elephants teeth (ie increase or decrease in number so regular) - reflecting on the curious series in the Trogon's tail-coverts? & with appearance in crest - in the gradual increase & assumption of colours in Eupheria (Australian small parrots) & many such facts, I must conclude, the variation is not quite irregular but follows some laws, wholly unknown - that such laws play a far more important part, than I have hitherto attributed to them. Such laws may be compared, with monsters appearing by law, though such bizarre monsters & apparently so anomalous - analogous cases appearing in different species - the law may be instanced by tuft on ducks head, & Fowls heads - feathers on Bantam's legs &c &c – Feathers on legs in Pidgeon & Poultry. Seeing that the series of Trogon-tail, though with some great gaps, all now existing - seeing that the series of Mastodons teeth do not go with

[in margin:] varying like other species of genera in case these be always returning to Embryonic forms

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than age - namely those most like other Pachydermata (using the American species) are not the oldest - makes it important to show that many species may be formed at all different ages & yet each have a succession at same time - vis same way as variations may be formed at different times & yet all be coexistent (case with Pears) Autumn Bergamot believed from time of Romans)

There is a great difficulty in such cases as Trogon-tail feathers; by my theory longest tail-coverts produced by (sexual) selection from shorter ones, so that in same country, the species with shorter tails shd be beaten out & extinguished; yet we have a nearly perfect living series; I can understand how at different times & places a variation in tail-feathers (from external conditions & selection) could be effected, but how can a series be selected.

The descendants from a species with little produced tail-coverts must have tendency to yield long flowing tail-coverts & this has been effected in different degrees in different

[in margin:] Can a series be shown in varieties of any plants from same parents?