Under domestication there would be a suspension of the previous elimination of reduced breastbones by natural selection (Weismann's panmixia), and a diminution of the parts concerned in flying might even be favoured, as lessened powers of continuous flight would prevent pigeons from straying too far, and would fit them for domestication or confinement. Such causes might reduce some of the less observed parts affected by flying, while still leaving the wing of full size for occasional flight, or to suit the requirements of the pigeonfanciers. A change might thus be commenced like that seen in the rudimentary keel of the sternum in the owl-parrot of New Zealand, which has lost the power of flight although still retaining fairly-developed wings.

the rock-pigeon in size. We can hardly suppose that use-inheritance especially affects the eight breeds that have varied most in size. If we exclude these, there is only a total shortening of 7 per cent. to be accounted for.

SHORTENED FEET IN PIGEONS.

Darwin thinks it highly probable that the short feet of most breeds of pigeons are due to lessened use, though he owns that the effects of correlation with the shortened beak are more plainly shown than the effects of disuse.1 But why need the inherited effects of disuse be called in to explain an average reduction of some 5 per cent., when Darwin's measurements show that in the breeds where long beaks are favoured the principle of correlation between these parts has lengthened the foot by 13 per cent. in spite of disuse?

SHORTENED LEGS OF RABBITS.

In the case of the domestic rabbit Darwin notices that the bones of the legs have (relatively) become shorter by an inch and a half. But

1 Variation of Animals and Plants under Domestication, i. 183,

as the leg-bones have not diminished in relative

1

weight, they must clearly have grown thicker

or denser. If disuse has shortened them, as Darwin supposes, why has it also thickened them? The ears and the tail have been lengthened in spite of disuse. Why then may not the ungainly hind-legs have been shortened by human preference independently of the inherited effects of disuse? By relying on apparently favourable instances and neglecting the others it would be easy to arrive at all manner of unsound conclusions. We might thus become convinced that vessels tend to sail northwards, or that a pendulum oscillates more often in one direction than in the other. It must not be forgotten that it would be easy to cite an enormous number of cases which are in direct conflict with the supposed law of use-inheritance.

1 Variation of Animals and Plants under Domestication, i. 130, 135; ii. 288.

BLIND CAVE-ANIMALS.

Weak or defective eyesight is by no means rare as a spontaneous variation in animals, "the great French veterinary Huzard going so far as to say that a blind race [of horses] could soon be formed." Natural selection evolves blind races whenever eyes are useless or disadvantageous, as with parasites. This may apparently be done independently of the effects of disuse, for certain neuter ants have eyes which are reduced to a more or less rudimentary condition, and neuter termites are blind as well as wingless. In one species of ant (Eciton vastator) the sockets have disappeared as well as the eyes. In deep caves not only would natural selection cease to maintain good eyesight but it would persistently favour blindness-or the entire removal of the eye when greatly exposed, as in

the cave-crab-and as Dr. Ray Lankester has

indicated, there would have been a previous selection of animals which through spontaneous weakness, sensitiveness, or other affection of the eye found refuge and preservation in the cave, and a subsequent selection of the descendants whose fitness for relative darkness led them deeper into the cave or prevented them from straying back to the the light with its various dangers and severer competition. Panmixia, however, as Weismann has shown, would probably be the most important factor in causing blindness.

INHERITED HABITS.

Darwin says:

"A horse is trained to certain

paces, and the colt inherits similar consensual movements." 2 But selection of the constitutional

1 Encyclopædia Britannica, article "Zoology."

2 Variation of Animals and Plants under Domestication, ii. 367.