the purposes of merely historical psychology as would be a full understanding of the causal connection, if there is any such connection to be understood.

So much, then, for the physical conditions under which consciousness is always and only found to occur. It remains briefly to conclude this chapter by showing that these conditions may most reasonably be regarded as first arising within the limits between which I have represented the origin of consciousness.

Remembering what has already been said concerning the gradual or undefined manner in which consciousness probably dawned upon the scene of life, and that I therefore represent its rise as occupying a wide area on the diagram instead of a definite line, I think it least objectionable to place the beginning of this dawn in nervous adjustments or reflex action, and the end of it in the association of ideas. For, on the one hand, it is clear from what has been said that it is impossible to draw any definite line between reflex and conscious action, inasmuch as, considered objectively or as action, the latter differs from the former, not in kind, but only in a gradual advance in the degree of central co-ordination of stimuli. Therefore, where such central co-ordination is first well established, as it is in the mechanism of the simplest reflex act, there I think we may with least impropriety mark the advent of consciousness. On the other hand, where vague memory of past experiences first passes into a power of associating simple ideas, or of remembering the connections between memories, there I think consciousness may most properly be held to have advanced sufficiently far to admit of our regarding it as fairly begun.

In this scheme, therefore-which of course it is needless to say I present as a somewhat arbitrary estimate where no more precise estimate is possible-the Colenterata are represented as having what Mr. Spencer calls "the raw material of consciousness," the Echinodermata as having such an amount of consciousness as I think we may reasonably suppose that they possess, if we consider how multifarious and complicated their reflex actions have become, and if we remember that in their spontaneous movements the neuromuscular adjustments which they exhibit almost present the appearance of being due to intelligence. The Annelida I

See Phil. Trans., Croonian Lecture, 1881.

place upon a still higher level of consciousness, because, both from the facts mentioned in "Animal Intelligence" and from those published by Mr. Darwin, it seems certain that their actions so closely border on the intelligent that it is difficult to determine whether or not they should be classed as intelligent. Upon this level, also, I represent the period of the embryonic life of Man as coming to a close; for although the new-born child, from the immaturity of its experience, displays no adjustments that can be taken as indicative of intelligence, still, as its nerve-centres are so elaborate (embodying the results of a great mass of hereditary experience, which although more latent in the new-born child than in the new-born of many other mammals and all birds, must still, we should infer from analogy, count of something), that we can scarcely doubt the presence of at least as much consciousness as occurs among the annelids. Moreover, pain appears to be felt by a new-born child, inasmuch as it cries if injured; and although this action may be largely or chiefly reflex, we may from analogy infer that it is also in part due to feeling. The remaining levels occupied by the dawn of consciousness may be considered as assigned to the lower Mollusca-an assignment which I think will be seen to be justified by consulting the evidence given in my former work of actions. performed by these animals of a nature which is unquestionably intelligent.

See his work on Earthworms, 1881.

A

CHAPTER VII.

SENSATION.

/By Sensation I mean simply Feeling aroused by a stimulus.

In my usage, therefore, the term is of course exclusive of all the metaphorical meanings which it presents in such applications as "sensitive plates," &c. It is also exclusive, on the one hand, of Reflex Action, as well as of non-nervous adjustments, and on the other, of Perception. Thus, too, it is exclusive of the carefully defined meaning which it bears in the writings of Lewes. He defined Sensation as the reaction of a sense-organ, whether or not accompanied by Feeling, and thus he habitually speaks of unfelt sensations. In his nomenclature, therefore, Sensation is a process of a purely physical kind, with which consciousness may or may not be involved. In my opinion, however, it is most desirable, notwithstanding his elaborate justification of this use of the term, to abide by its original signification, which I have explained. When I have occasion to speak of the physical reaction of a senseorgan, I shall speak of it as a physical reaction, and not as a sensation. The distinction which, in common with other psychologists, I draw between a Sensation and a Perception, I shall explain more fully in the chapter where I shall have to treat of Perception. Meanwhile it is enough to say that the great distinction consists in Perception involving an element of Cognition as well as the element of Feeling

It is more difficult to draw the distinction between Sensation and non-nervous adjustments, and still more so between Sensation and nervous adjustments which are unfelt (Reflex Action). Here, however, we are but again encountering the difficulty which we have already considered, viz., that of drawing the line where consciousness begins; and, as we have previously seen, this difficulty has nothing to do with the validity of a classification of psychical

faculties; it only has to do with the question whether such and such a faculty occurs in such and such an organism. Therefore, so long as the question is one of classifying psychical faculties, we can only say that/wherever there is Feeling there is Sensation, and wherever there is no Feeling there is no Sensation. But where the question is one of classifying organisms with reference to their psychical faculties, it is clear that the difficulty of determining whether or not this and that particular low form of life has the beginnings of Sensation, is one and the same as the question whether it has the beginnings of Consciousness Now we have already considered this question, and we have found it impossible to answer; we cannot say within broad limits where in the animal kingdom consciousness may first be regarded as present. But for the sake of drawing the line somewhere with reference to Sensation, I draw it at the place in the zoological scale where we first meet with organs of special sense, that is to say, at the Colenterata. In doing this, it is needless to observe, I am drawing the line quite arbitrarily. On the one hand, for anything that is known to the contrary, not only the sensitive plant which responds to a mechanical stimulus, but even the protoplasmic organisms which respond to a luminous stimulus by congregating in or avoiding the light, may, while executing their responses, be dimly conscious of feeling; and, on the other hand, the mere presence of an organ of special sense is certainly no evidence that its activities are accompanied by Sensation. What we call an organ of special sense is an organ adapted to respond to a special form of stimulation; but whether or not the process of response is accompanied by a sensation is quite another matter. We infer by a strong analogy that it is so accompanied in the case of organisms like our own (whether of men or of the higher animals); but the validity of such inference clearly diminishes with the diminishing strength of the analogy-i.e., as we recede in the zoological and psychological scales from organisms like our own towards organisms less and less like.

Having thus made it as clear as I can that it is only for the matter of convenience that I have supposed the rise of Sensation to coincide with the rise of organs of special

Although this sounds like a truism, it is in direct opposition to the classification of Lewer, alluded to above.

sense, I shall next proceed to take a brief survey of the animal kingdom with reference to the powers of special sense. In doing this, however, it is needless, and indeed undesirable, that I should enter with much closeness into the anatomy of the innumerable organs of special sensation which the animal kingdom presents. My object is merely to give a general outline of the powers of special sensation probably enjoyed by different classes of animals; for, as these powers constitute the foundation of all the other powers of mind, it is of importance for us to have a general idea of the grade of their development in the sundry grades of the zoological scale.

In some of his recently published experiments, Engelmann found that many of the protoplasmic and unicellular organisms are affected by light; that is to say, their movements are influenced by light, in some cases causing acceleration, in others slowing, of their movements; in some cases the organisms seeking the light, while in other cases they shun it, &c., &c. He found that all these effects were reducible to one or other of three causes: (1) alteration produced by the light in the interchange of gases, (2) consequent alteration in the conditions of respiration, and (3) specific processes of luminous stimulation. It is with the latter only that we are concerned, and the organism which Engelmann names as exhibiting it typically is Englena viridis. precautions had been taken to eliminate causes 1 and 2, it was still found that this organism sought the light. Moreover, it was found that it would only do so if the light were allowed to fall upon the anterior part of its body. Here there is a pigment-spot, but careful experiment showed that this was not the point most sensitive to light, a colourless and transparent area of protoplasm lying in front of it being found to be so. Hence it is doubtful whether this pigmentspot is or is not to be regarded as an exceedingly primitive organ of special sense. Of the rays of the spectrum, Englena

viridis prefers the blue.*

The remarkable observation recorded by Mr. H. J. Carter, F.R.S., and quoted from him in my previous work,† seems to display almost incredible powers of special sense among the

For full account of these experiments, see Pflüger's Archiv. f. d. ges. Physiologie, Bd. XXIX, 1882.

Animal Intelligence, pp. 19-21.