198 CLOSE OF THE PRE-EVOLUTIONARY PERIOD 



among the organs and by their consequent differentiation. 

 An animal is like a workshop where some complicated 

 product is manufactured, and the organs are like the 

 workmen. Each workman has his own special piece of 

 work to do, at which he becomes thoroughly expert ; and the 

 finished product is manufactured more rapidly and efficiently 

 by the co-operation of workers each skilled in one department 

 than it would be if each workman had to produce the whole. 

 Applied to the organism this principle of the division 

 of labour means the differentiating out of the separate 

 functions, their localisation in different parts of the 

 organism, and their co-ordination to produce a combined 

 result. 



This differentiation of functions implies a corresponding 

 differentiation of organs, but it is functional differentiation 

 which always takes the lead. " Where division of labour has 

 not been introduced into the organism there must exist 

 a great simplicity of structure. But just as uniformity in the 

 functions of the different parts of the body implies a 

 uniformity in their mode of constitution, so diversity in 

 function must be accompanied by particularities in structure; 

 and, in consequence also, the number of dissimilar parts 

 must be augmented and the complication of the machine 

 increased " (p. 463). Since function comes before form there 

 is not always a special organ for every function. "It is 

 a grave error to believe that a particular function can 

 be performed only by one and the same organ. Nature can 

 arrive at the desired result by various ways, and when we 

 look down through the animal kingdom from the highest to 

 the lowest forms we see that the function does not disappear 

 even when the special instrument provided for the purpose 

 in the higher types ceases to exist" (p. 470). 



Nature, holding fast to the law of economy, does not even 

 always create a new organ for a new function ; she may 

 simply adapt an undiffcrentiated part to special functions, or 

 she may even convert to other uses an organ already 

 specialised (p. 464). So, for example, the function of respira- 

 tion is in the lowest animals diffused indifferently over 

 the whole surface of the body, and only as organisation 

 advances is it localised in special organs, such as gills. Now 



