Nov., 1890. 
ORGANIC DEATH. 
243 
An individual consists of an aggregation of matter, 
whether in the simplest or most complex form, the whole 
of which is under the control of a single will. Parts of that 
aggregate may be cut off and perish, leaving the controlling 
will intact, but when the entire individual dies the controlling 
will vanishes. A species consists of an aggregation of indi¬ 
viduals, but, as far as we know, they are not controlled by any 
single specific will, so that, though all the individuals should 
die, leaving no representative of the species, yet no actual 
thing would vanish except those individuals. 
In man there is direct consciousness of his individuality. 
In the other vertebrates there is at least the consciousness of 
sensation. How far down in the scale of being anything 
which can properly be called consciousness exists we do not 
know, but the mental faculty must be present in all animals 
and probably in plants also, for no possible line can be drawn 
anywhere between the Amceba and the Ape, above which 
mental faculty can be supposed to have its beginning. The 
first phenomenon of individual death is the disappearance of 
this mental faculty. The separation of the aggregated 
material follows afterwards. But in the death of a species 
there is no such first stage. The entire phenomenon is com¬ 
prised in the separation and disappearance of the aggregated 
individuals. This difference is a very important one, and as 
the death of a species is not threfore strictly analogous to the 
death of an individual, so the life of a species may not be sub¬ 
ject to that law of periodicity which so evidently controls in¬ 
dividual life. But is there any evidence of periodicity in species, 
genera, and other groups, from such knowledge of their history 
as we are able to obtain, not from personal observation only, but 
with all the resources of science ? Periodicity, in the sense in 
which I am using that word, may be defined as a tendency to 
pass through a series of changes within a definite time, the 
scheme of changes and the period within which they are to 
be executed being predetermined in the constitution of the 
organism. 
There is ample geological evidence that within the limits 
of each great sub-kingdom of animal and vegetable life there 
has been a successive change of genera, and that within the 
limits of each genus there has been a similar successive 
change of species. 
If it can be shown that the scheme of these changes, 
whether in genus, species, or individual, is distinctly 
analogous; that the order in which certain characters 
succeed each other is constant; that the beginning, the 
middle, and the ending of each developing group bear always, 
