BEHAVIOUR OF CELLS TL 
functional activities being stimulated or checked by many 
- influences ; and yet this varied life may give no evidence of a 
guiding consciousness : if purpose there be, it lies deeper than 
its protoplasm, deeper than the dim sentience which may be 
present or may be absent—we cannot tell which. 
And when the cells are incorporated in the body of one of 
the higher animals, instead of each preserving a free and 
nomad existence; when they become the multitudinous con- 
stituents of an organic republic with unity of plan and unity 
of biological end, then the behaviour of each is limited in range 
but perfected within that range, in subservience to the require- 
ments of the more complex unity. The muscle cell contracts, 
the gland-cell secretes, the rods and cones of the retina respond 
to the waves of light, and all the normal responses of the 
special cells go on with such orderly regularity that the term 
behaviour seems scarcely applicable to reactions so stereotyped. 
But the physiologist and the physician know well that such 
uniformity of response is dependent on uniformity of conditions. 
A little dose of some drug will profoundly modify and render 
abnormal the procedure which was before so mechanical in its 
exactitude ; and we are thus led to see how dependent the 
orderly behaviour really is on the maintenance of certain sur- 
rounding conditions. 
Moreover, the existence of every cell in the body corporate 
is the outcome of a process of division involving a special mode 
of behaviour in the nucleus, of which we are only beginning to 
euess the meaning and significance, and of which we seek in 
vain to find an explanation in mechanical terms. And when 
we trace these divisions back to their primary source in the 
fertilized ovum, we find changes and evolutions in the nuclear 
matter of which it can only be said that the more they are 
studied the more complex and varied do they appear. 
The egg, or ovum, is a single cell produced by the female, 
and varying much in size, according to the amount of 
food-yolk with which it is supplied. Like other cells, it has 
a nucleus, and this undergoes changes which are definitely 
related to the fertilization of the ovum, which we describe as 
