CONTINUITY IN EVOLUTION 329 
marshalled and ordered in embryological development ; definite 
tissues are formed ; the stages of their genesis can be pre- 
dicted with accuracy ; and in due time a puppy is born which 
shall grow to the likeness of its parents and behave as they 
behaved. We can trace the succession of events; we see 
that they form a related series; we have good reason for 
believing that the state of matters at any one moment is the 
antecedent condition of the state of matters at the succeeding 
moment. More than this science cannot say. The underlying 
cause is, for science, hidden in the mists of the unknown. Even 
for metaphysics it is but part of the force that beats through 
the universe and makes it not a chaos but a cosmos—a force 
known to us only in its effects. 
It will thus be seen that the conception of continuity in 
organic evolution has, broadly considered, a threefold aspect. 
First, there is the continuity of the germinal substance through 
whose reproductive behaviour under the appropriate conditions 
embryological development occurs; secondly, there is con- 
tinuity in this. embryological development, stage by stage, 
from the fertilized ovum to the adult which is its final product 
and expression ; thirdly, there is continuity in these final pro- 
ducts, in the animals whose organic, instinctive, and intelli- 
gent behaviour lie open to our study and investigation. The 
first is germinal, the second developmental, the third evolu- 
tional continuity. 
Before attempting to summarize some of the contributions 
afforded by our inquiry towards the doctrine of continuity in 
the last of these three aspects, we must pause for a moment to 
consider how far and in what sense continuity can be predi- 
cated of mental development. 
We have regarded the conscious situation as the psychical 
aspect of a nerve-situation in the sensorium ; and the nervous 
system, capable of behaving in this way, is in developmental 
continuity with the germinal substance of the fertilized ovum. 
But what shall we say with regard to the psychical aspect ? 
Two hypotheses seem open to us, each of which presents diffi- 
culties, but of different kinds. The first is, that when the 
