4. How far down the scale of animal life the phenomena of consciousness are manifested, it is impossible to say. No one doubts their presence in his fellow-men; and, unless any strict Cartesians are left, no one doubts that mammals and birds are to be reckoned creatures that have feelings analogous to our smell, taste, sight, hearing, touch, pleasure, and pain. For my own part, I should be disposed to extend this analogical judgment a good deal further. On the other hand, if the lowest forms of plants are to be denied consciousness, I do not see on what ground it is to be ascribed to the lowest animals. I find it hard to believe that an infusory animalcule, a foraminifer, or a fresh-water polype is capable of feeling; and, in spite of Shakspere, I have doubts about the great sensitiveness of the "poor beetle that we tread upon." The question is equally perplexing when we turn to the stages of development of the individual. Granted a fowl feels; that the chick just hatched feels; that the chick when it chirps within the egg may possibly feel; what is to be said of it, on the fifth day, when the bird is there, but with all its tissues nascent? Still more, on the first day, when it is nothing but a flat cellular disk? I certainly cannot bring myself to believe that this disk feels. Yet if it does not, there must be some time in the three weeks, between the first day and the day of hatching, when, as a concomitant, or a consequence, of the attainment by the brain of {43} the chick of a certain stage of structural evolution, consciousness makes its appearance. I have frequently expressed my incapacity to understand the nature of the relation between consciousness and a certain anatomical tissue, which is thus established by observation. But the fact remains that, so far as observation and experiment go, they teach us that the psychical phenomena are dependent on the physical. In like manner, if fishes, insects, scorpions, and such animals as the pearly nautilus, possess feeling, then undoubtedly consciousness was present in the world as far back as the Silurian epoch. But, if the earliest animals were similar to our rhizopods and monads, there must have been some time, between the much earlier epoch in which they constituted the whole animal population and the Silurian, in which feeling dawned, in consequence of the organism having reached the stage of evolution on which it depends.