In the following cells there is shown the increase in amount of the male material and the final intimate commingling in _g_ which precedes the first segmentation.

_g_ represents a new organism formed by the union of the male or female cell but differing from either of them.] Living matter is always individual, and this individuality is expressed in slight structural variations from the type of the species as shown in an average of measurements, and also in slight variations in function or the reactions which living tissue shows towards the conditions acting upon it.

The anatomical variations are more striking because they can be demonstrated by weight and measure, but the functional variations are equally numerous.

Thus, no two brains react in exactly the same way to the impressions received by the sense organs; there are differences in muscular action, differences in digestion; these variations in function are due to variations in the structure of living material which are too minute for our comparatively coarse methods of detection.

In the enormous complexity of living matter it is impossible that there should not be minute differences in molecular arrangement and to this such functional variations may be due.