186 NOTICES OF THE MEETINGS [April 30, 
ganized being has been formless and will again be formless ; the indi- 
vidual animal or plant is the swm of the incessant changes, which 
succeed one another between these two periods of rest. 
The individual animal is one beat of the pendulum of life, birth 
and death are the two points of rest, and the vital force is like the 
velocity of the pendulum, a constantly varying quantity between 
these two zero points. The different forms which an animal may 
assume correspond with the successive places of the pendulum. 
In man himself, the individual, zoologically speaking, is not a 
state of man at any particular moment as infant, child, youth or 
man; but the sum of all these, with the implied fact of their definite 
succession. 
Tn this case, and in most of the higher animals, the forms or 
states of the individual are not naturally separated from one another : 
they pass into one another, undistinguishably. 
Among other animals, however, nature draws lines of demarcation 
between the different forms ; thus, among insects the individual takes 
three forms, the caterpillar, the chrysalis, and the butterfly. These, 
do not pass into one another insensibly, but are separated by appa- 
rently sudden changes ; each change being accompanied by a sepa- 
ration of the individual into two parts. One part is left behind and 
dies, it receives the name of a skin or cast; the other part con- 
tinues the existence of the individual under a new form. 
The whole process is called Ecdysis: it is a case of what might 
be termed concentric fission. 
The peculiarity of this mode of fission is; that of the two portions 
into which the individual becomes divided at each moult, one is 
unable to maintain an independent existence and therefore ceases to 
be of any importance ; while the other, continues to carry on all 
the functions of animal life and to represent in itself the whole 
individuality of the animal. From this circumstance there is not 
objection to any independent form being taken for, and spoken of 
as the whole individual, among the higher animals. 
But among the lower animals the mode of representation of the 
individual is different and any independent form ceases, in many 
cases, to represent the whole individual ; these two modes, how- 
ever, pass into one another insensibly. 
The best illustration of this fact may be taken from the develop- 
ment of the Echinodenus, as it has been made known by the brilliant 
discoveries of Professor Miiller. 
The Echinus lividus stands in the same relation to its Pluteus, as 
a butterfly to its caterpillar; in the course of development only a 
slight ecdysis takes place, the skin of the Pluteus becoming for the 
most part converted into the skin of the Echinus. 
But in Asterias, the Bipinnaria which corresponds with the Plu- 
teus, gives up only a portion of its integument to the developed 
Asterias; the remaining and far larger portion lives for a time after 
its separation as an independent form. 
