174 Thomas Huxley, Esq., on Animal Individuality. 



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 im- 

 plied fact of their definite succession. 



In 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 de- 

 marcation 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 insen- 

 sibly, but are separated by apparent sudden changes ; each 

 change being accompanied by a separation of the individual 

 two parts. One part is left behind and dies ; it receives the 

 name of a skin or cast : the other part continues the exist- 

 ence 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 ani- 

 mal. From this circumstance, there is no objection to any 

 independent form being taken for, and spoken of as, the 

 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, however, pass into one another insensibly. 



The best illustration of this fact may be taken from the 

 development 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 



