the 12th day, and the movements in which the head and face parts are concerned can be induced by electrical stimulation about this time. It is to be specially noted that these movements can be produced in the rabbit, experimentally, almost as soon as those of the fore-limb-in fact, I question whether, in some cases at least, they are not excitable earlier and with greater facility, i.e. with a weaker current. With the hind-legs the case is altogether different-in fact, my investigations would lead me to infer that the hind-legs are never related to the cortex in the same way as the fore-limbs. In no case have I been able to establish to my satisfaction the existence of a cortical centre for the hind-legs of the same nature (to put the matter cautiously) as those for the fore-limbs, head, face, etc. The relation between the early, and all but simultaneous, development of the cortical centre for the fore-limbs. and head (and face) parts, and the physiological and psychic manifestations of the young rabbit afford one of the most beautiful and striking illustrations of correlation known to me.

IV. THE CAVY, OR GUINEA-PIG.

THE Cavy comes into the world able to take care of itself. It can, in a few hours, if not at once, run about quite well, eat, etc. It is at the set-out as far on in the path of development as a rabbit some days after its eyes are open, though in the end there is little difference between these two rodents physically or otherwise.

Corresponding with this advanced physiological and psychic development, the cortex is, as I have shown, excitable at or soon after birth, so that here again there is rendered evident by experiment a close correlation of the kind considered throughout this paper.

V.-BIRDS.

ONE learns how large a proportion of the possibilities, physiological if not psychic, in the pigeon are not dependent on the cerebral cortex, or even the entire cerebrum, by ablation of the latter. Movements, though not spontaneous, are nearly as perfect afterwards as before, and much light is thrown on the nature of reflexes.

I have, after careful investigation, been unable to find any motor cortical centres whatever. The whole cerebral cortex appears to be absolutely inexcitable, except, perhaps, as concerns certain eye movements, and as for these a strong stimulus is required, it is doubtful if they are of cortical origin in the usual sense of the term.

Nevertheless, unless we deny the existence of voluntary movements to the bird-an extreme position -we are landed in physiological difficulties, inasmuch as it has been assumed by nearly all physiologists that the cortex is essential to voluntary movements. The case of the bird seems to me to show that we have much to learn as to the nervous mechanism of voluntary movements, notwithstanding all the investigation that has been given to this subject.

Conclusions.

In the dog and the cat there is a period, extending from birth to about the time of the opening of the eyes, characterised by reflex movements, the sway of instincts, and the absence of intelligence. During this time the cerebral cortex is inexcitable by electrical stimulation, so that the psychic condition during the blind period is correlated with an undeveloped state of the motor

centres of the cortex of the cerebrum. The advance in movements, first of the limbs, and later of the head and face parts, together with the psychic progress associated with this, is correlated with the rapid development of the cortical centres for the limbs in the first instance, and later, for the head and face in the period immediately following the blind stage.

This is more rapid and more pronounced in the cat than in the dog, and is correlated with the greater control in the cat over the fore-limbs and with certain physiological and psychic developments characteristic of the cat.

Similar conclusions apply to the rabbit, except that the difference in the rapidity of development of head and face movements is correlated with an earlier organisation of the corresponding cortical centres, and that there is a greater difference between the fore-limb and the hind-limb, with all of which there are special psychic correlations bound up with certain peculiarities of the rabbit's modes of life.

The vast difference in physiological and psychic development of the cavy at birth is correlated with the presence of cortical cerebral centres, readily excited by artificial stimuli, centres which in a few days reach a practically perfect state of development.

The psychic manifestations of the pigeon and the fowl have not the same sort of cerebral cortical correlates as the animals referred to above.

PART IV.

DISCUSSIONS ON INSTINCT.

PROF. C. LLOYD MORGAN ON INSTINCT.

TO THE EDITOR OF Science-In an account of a discussion on "Instinct," given in Science of 14th February, Prof. Morgan is reported thus: "He described his own interesting experiments with chicks and ducklings, and held that these and other evidence tend to show that instincts are not perfected under the guidance of intelligence, and then inherited. A chick will peck instinctively at food, but must be taught to drink [Italics mine]. Chicks have learned to drink for countless generations, but the acquired action has not become instinctive."

In one of a series of papers now in the Press on "The Psychic Development of Young Animals and its Physical Correlation," I have given in detail an account of a study of the pigeon and the chick. It so happens that this very question of drinking by chicks has been especially noted, and I find a record of one observation to the effect that a newly-hatched chick, pecking at the drops on rim of a vessel containing water, accidentally got its beak into the liquid, whereupon it at once raised its head and drank perfectly well in the usual fashion for fowls. Was this by teaching or by instinct? Later, the chicks seem to peck and drink, sometimes on seeing the mother do so. The act seems to be, in

such a case, a sort of imitation, so far as its inception is concerned. But will any one contend that that first act of drinking, referred to above, was other than instinctive? Again, when a chick first drinks, on its beak being put into water, can the act be considered as the result of teaching? Is the chick so intelligent as to carry out an act so complex in such a perfect way, as it does on the very first occasion, as the result of "teaching"? Surely no one will deny that sucking is an instinctive act, yet a newly - born mammal sucks only when its lips come in contact with the teat. Is not the case very similar with the chick? The only difference is, that the chick is slower to recognise water than food, but as soon as the beak touches water it drinks, and there is no teaching about it. Considering how seldom a fowl drinks, yet pecks all day long at particles of food, it is not surprising that the chick is slower to recognise water (drink) than food. But it is one thing to say that a chick learns to recognise drink, and another to affirm that it learns to drink. The process of drinking is quite as perfect as that of eating from the very first, if not more so, for a chick at first often misses what it pecks at, and fails to convey the object into its mouth in other cases, though it may

touch it.

The view that instincts are perfect from the first, and undergo no development from experience, I believe, after much observation, to be as erroneous as it is ancient.

Instinct is never, perhaps, perfect at first, and, so far as I can see, could not be owing to general imperfect development in the animal of motor power, the senses, etc. A young puppy will suck anything almost that can pass between his lips, as a chick will peck at any light spot or object if small, be it food or not. My