Geographical Distribution Continued 14. Morphology, Embryology, Rudimentary Organs 15. 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.
Breeders believe that long limbs are almost always accompanied by an elongated head.
Colour and constitutional peculiarities go together, of which many remarkable cases could be given amongst animals and plants. Hence if man goes on selecting, and thus augmenting, any peculiarity, he will almost certainly modify unintentionally other parts of the structure, owing to the mysterious laws of correlation. Any variation which is not inherited is unimportant for us. But the number and diversity of inheritable deviations of structure, both those of slight and those of considerable physiological importance, are endless. Dr. Prosper Lucas's treatise, in two large volumes, is the fullest and the best on this subject.