14 COMPARATIVE ANATOMY. 



in this case represents, potentially, a collection of organs, which 

 only appear, in fact, when the different functions are no longer 

 performed by every part of the body. The condition which the 

 lower organisms permanently exhibit in regard to this matter is 

 possessed for a short time only by the more complicated. 



Differentiation. 



§ 12. 



The complication of the organism arises from a process of 

 division which transfers to separate parts the physiological acti- 

 vities of the primitively homogeneous body. What was previously 

 accomplished by the whole body, is, subsequently to that process, 

 carried out by particular portions. The work is then done either by 

 a laro-e number of parts, which are distinct from but similar to one 

 another, or the separate parts acquire dissimilar shapes, and become 

 different from one another. In the first case the division of labour 

 is quantitative, in the latter it is qualitative, and the separation 

 of the different parts is in correspondence with a difference in func- 

 tion. According to the degree in which the separation or division 

 originally set up in the primitively indifferent body is repeated in the 

 organs derived from it, further complications arise, which present 

 for our observation a step-by-step progression in development. 

 Hence there arises a difference in the value of the organs, and it 

 becomes necessary to distinguish their higher and lower conditions. 



The distribution of work amongst a number of different organs 

 leads to the perfecting of the operations of such organs. Each 

 organ is enabled to develop in a definite direction, in correspond- 

 ence with the particular function which is undertaken by it. The 

 organism thus becomes more highly developed, as well as com- 

 plicated. Division of labour leads to a perfecting of the whole 

 organism. According as the division of labour involves only a 

 few or many organs, a greater or less part of the organism is 

 brought under the operation of this perfecting influence. The 

 greater the importance, for the whole organism, of the organs 

 affected, the more considerable is the perfecting accomplished in 

 it through their modification. The functions which attach them- 

 selves to definite parts of the body bring about a difference in the 

 development of those parts proportionate to their own difference ; and 

 thus it is that new parts and new organs arise, which are different 

 from those already existing. The division of functions leads to the 

 establishment of a difference, that is to a differentiation, of the 

 parts. A part of the body which was formerly like the rest, and con- 

 sequently not different from it — that is was indifferent — passes into 

 the condition of being separate, becomes distinguishable, or different 

 from the rest. And as this differentiation is connected with the 

 division of labour, inasmuch as it is conditioned by it, it may be 

 regarded as the product of it. Every physiological function can be 

 again divided qualitatively into various sub-functions, by the locali- 



