148 UPON ANIMAL INDIVIDUALITY 



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. 



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 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 separa- 

 tion 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 continues 

 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 individu- 

 ality 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, however, 

 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 briUiant 

 discoveries of Professor M tiller. 



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 Pluteus 

 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. 



