1902.] NATURAL SCIENCES OF PHILADELPHIA. 193 



geny, can be delennined only by considering in addition the ener- 

 gies and activities of organisms, and their interaction with the 

 environment. 



II. The Individual. 



Organisms are living entities, yet, since each organism is known 

 fo be composed of parts, there arises the necessity of determining 

 the degree or kind of individuals that are to be classified. In 

 Nature occur only individuals, as was clearly pointed out by La- 

 marck, and is generally acknowledged at the present time, 

 species and other groups being arbitrary concepts. Hence it 

 is individuals that are to be classified and mentally arranged into 

 groups characterized by similarity of structure ; but before this can 

 be done it is necessary to decide what is meant by the term " indi- 

 vidual. ' ' 



The primary idea of an individual is independence, as in saying 

 ' ' an individual is that which is capable by itself of performing all 

 the activities necessary for its existence" ; or " that which cannot 

 be subdivided without ceasing to be." But neither of these state- 

 ments are quite correct, for no organism is wholly independent of 

 other organisms and of its environment, and experiment has 

 shown (in cases of regeneration) that what are commonly kno^vu 

 as individuals may be subdivided, and yet not cease to exist ; the 

 independence then is one of relative degree. Another criterion is 

 that of structural disassociation : an indi\'idual is an organism struc- 

 turally complete in itself, not a part of a larger structural whole ; 

 though in practice this definition is often found of little value, as 

 in organisms forming corms and stocks, yet perhaps it is as far- 

 reaching as any that can be offered. Another criterion would be 

 the ability of reproducing itself through an ontogenetic cycle simi- 

 lar to that by which it had been formed. Yet, with this definition 

 difficulties at once arise. For while, e. g., the ovum of a bird, 

 once fertilized, can form an adult bird containing ova in its 

 ovary, the last-named ova are unable to give rise to a second gener- 

 ation of adult birds until they are first fertilized. And the adult 

 hen bird cannot produce a new generation until its ova are fertilized 

 by spermatozoa from the male. The ovum of a bird, deposited 

 outside the body of the mother, would generally be regarded as an 

 individual, and so would the adult hen or cock ; but the ovum can - 

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