Apeil 14, 1916] 



SCIENCE 



523 



ologieal individual which I have tried to 

 present. 



C. M. Child 



University op Chicago 



THE BASIS OF INDIVIDUALITY IN 

 ORGANISMS FROM THE STAND- 

 POINT OF CYTOLOGY AND 

 EMBRYOLOGYi 



I 

 An individual in the broadest sense is 

 any animate or inanimate thing which is 

 regarded as a unit. In this sense the elec- 

 tron, atom, molecule, crystal, biophore, de- 

 terminer, chromomere, chromosome, nu- 

 cleus, eentrosome, cell, organ, system, 

 person, corm, state, species, etc., are in- 

 dividuals. In all but the simplest units 

 individuality involves organization, that 

 is differentiation into parts and integra- 

 tion into a single whole. A fundamental 

 property of any unit is its separateness or 

 separableness, from other units, and yet no 

 unit is completely independent. Biological 

 units are separate in both structure and 

 function from other units and yet they are 

 related to others and these relations may 

 be of such a sort that they constitute units 

 of a higher order. Organic individuality 

 of whatever order is dependent upon sepa- 

 rateness of structure, of growth and of 

 division. But while all vital units are sep- 

 arate or separable, they vary greatly in in- 

 dependence from the parts of a cell which 

 are incapable of independent life to cells 

 and to persons which are capable by them- 

 selves of maintaining life processes. The 

 failure to distinguish between separate- 

 ness and independence has been a fruitful 

 source of misunderstandings in biological 

 controversies. 



1 Eead at a joint symposium of the American 

 Society of Zoologists and Section F of the Ameri- 

 can Association for the Advancement of Science, 

 Columbus, Ohio, December 30, 1915. 



An organic individual then is any unit 

 capable of manifesting the properties of 

 life. The simplest and most fundamental 

 properties of life are: (1) Metabolism, 

 especially assimilation and growth, and 

 (2) Reproduction by division. Every 

 vital unit manifests both of these proper- 

 ties from the ultra-microscopical units of 

 living matter to its more complex aggre- 

 gates. To these two properties there is 

 usually if not invariably added (3) sensi- 

 tivity or the capacity of responding to 

 stimuli, frequently in a beneficial or adap- 

 tive way. An organic individual then is 

 capable of assimilation, growth and di- 

 vision and it may be irritable or sensitive. 

 This definition can not be made more spe- 

 cific, for individuality is not a hard and 

 fast thing. There are all degrees of or- 

 ganic individuality from the simplest and 

 smallest units of living matter to the larg- 

 est and most complex. As applied to hu- 

 man beings and their organization into so- 

 ciety, the word "individuality" has come 

 to have a metaphysical and mystical signifi- 

 cance and not infrequently this mysticism 

 has been extended to all forms of individ- 

 uality. 



1. Individuality of Ultra-microscopic 

 Units of Living Matter. — Long ago Briicke 

 (1861) maintained that protoplasm must 

 be composed of ultra-microscopic units ca- 

 pable of assimilation, growth and division 

 and these units he called "the smallest liv- 

 ing parts." Many students of the subject 

 since that time have postulated similar 

 units; such as the "physiological units" 

 of Spencer, the "gemmules" of Darwin, 

 the "plasomes" of Wiesner, the "pan- 

 genes" of de Vries, the "idioblasts" of 0. 

 Hertwig, the "biophores" and "determi- 

 nants" of Weismann, and the "factors," 

 "determiners" and "genes" of many stu- 

 dents of heredity. Recent studies of Men- 



