Many laws regulate variation, some few of which can be dimly seen, and will hereafter be briefly discussed.
I will here only allude to what may be called correlated variation. Important changes in the embryo or larva will probably entail changes in the mature animal.
In monstrosities, the correlations between quite distinct parts are very curious; and many instances are given in
Isidore Geoffroy St-Hilaire's great work on this subject.
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| Isidore Geoffroy Saint Hilaire |
Breeders believe that long limbs are almost always accompanied by an elongated head.
Some instances of correlation are quite whimsical: thus cats which are entirely white and have blue eyes are generally deaf;
but it has been lately stated by Mr. Tait that this is confined to the males.
Colour and constitutional peculiarities go together, of which many remarkable cases could be given amongst animals and plants.
From facts collected by Heusinger, it appears that white sheep and pigs are injured by certain plants, whilst dark-coloured individuals escape:
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| sheep |
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| pig |