are perhaps less confident than their predecessors of the last century, for the solution in this direction has to face not only the problem of organic co-ordination already referred to, but also that of consciousness and mind.  For although the study of psychology on physiological lines has made similar progress to that of other branches of physiology, it seems to approach little nearer to a discovery of the nature of the relation between consciousness in its various aspects and the material body with which it is associated.  So long as this gulf remains unbridged, the possibility of a satisfactory mechanistic explanation of life seems far away.

On the other hand, there has been a revival of the ancient tendency towards what is called a vitalistic solution.  A certain number of biologists, impressed by the apparent similarity between the control and co-ordination exercised by the organism over its functions and the conscious control of voluntary activity with which we are familiar in ourselves, have supposed that these things are not merely superficially similar but have a real and fundamental affinity.  This does not mean that organic control is always conscious, but that there is a controlling entity, non-material in nature, which is similar in kind to the ‘ego’ of a self-conscious human being.  They suppose that the organism is not simply material, but is a material mechanism controlled by a non-material entity the nature of which is more akin to what we mean by the word spirit than anything else of which we are accustomed to think.  They are in fact dualists, and divide reality into the material and spatial on the one hand, and non-material principle or entity which may fairly be called spiritual on the other.

And, in the third place, there are those who seek a solution which denies the truth of both the preceding, and which is metaphysically idealist or monist in character.  To them, if the present writer understands their attitude, matter and spirit are different aspects of one reality.  In the inorganic and non-living, phenomena appear which are generalized under the laws of physics and chemistry, but the phenomena of life fall into a different category which includes the conception of co-ordination or individuality, while a still higher category is required to include the phenomena of consciousness and mind.

It is evident from this brief review that Biology in the period considered has passed through three main stages.  The first of these was the acceptance of a new illuminating and unifying idea, which led to enthusiastic research in many directions for the purpose of proving and amplifying it.  Very rapidly new facts, or new interpretations of facts already known, were shown to fall into line, and the evolution theory became converted from a hypothesis into something approaching a dogma.  Not only the idea of organic evolution itself, but all the current beliefs about the method of evolution, and the larger speculations