114 BIOLOGICAL LECTURES. 



with that of the egg. The organism is regarded rather as a 

 community of such individualities, bound together by inter- 

 action and mutual dependence. According to this view, de- 

 velopment does not consist in carrying forward continuous 

 changes in the same individual organization, but in multiplying 

 individualities, the complex of which represents, at every 

 stage, not tJie organism, but one of an ascending series of 

 organisms, which is to terminate in the adult form. 



In the egg-cell we are supposed to have an elementary organ- 

 ism ; in the two-cell stage, two elementary organisms, forming 

 together an organism of a totally different order, based on 

 a new scheme of organization. In" the four-cell stage we 

 have another organism, in the eight-cell stage another, and 

 so on. 



''Physiological division of labor," as Milne-Edwards first 

 phrased it, is unquestionably a principle of wide application. 

 Given the cells as morphological units and this physiological 

 principle, the evolution of a cellular organism, may be con- 

 ceived of as a most simple affair. From a simple colony of 

 like cells, we pass to a commonwealth of differentiated and 

 mutually dependent cells. A multitude of independent cell- 

 organisms, adopting mutual service as the best economy, find 

 themselves in the end incapable of independent life, and so 

 firmly bound together in interdependence, that they constitute 

 a complex individual. The usual conception of this division 

 of labor is, as Herbert Spencer 1 has recently stated it, "an 

 excliange of services,- an arrangement under which, while one 

 part devotes itself to one kind of action, and yields benefits to 

 all the rest, all the rest, jointly and severally performing their 

 special actions, yield benefits to it in exchange. Otherwise 

 described, it is a system of itiutual dependence." 



We habitually apply this anthropomorphic conception to 

 every grade of organization. The higher organism is regarded 

 as a colony of cells ; the cell as a colony of simpler units, 

 nucleus, centrosome, and so on ; the nucleus as a colony of 

 chromosomes ; the chromosome, according to Weismann's ter- 

 minology, as a colony of "ids"; the "id" as a colony of 



1 The Contemporary Review, February, March, and May, 1893. 



