34 INITIATIVE IN EVOLUTION 



do is to contribute in their measure to the metabolism of the 

 organism, being too numerous and minute to affect any structural 

 change. In a higher form of life none but those which are fre- 

 quently repeated in the individual and in succeeding generations 

 can effect any structural response. 



Mould and Sieve. 



It will be remembered that a single example was given of a 

 short-haired dog in which its common habit of lying was associated 

 with a certain pattern of hair. This introduces and illustrates 

 the very wide conception of a moulding process undergone by an 

 organism. It is one familiar to biologists and very much so to 

 Professor Thomson in his various writings. Not less is he an 

 exponent of the metaphorical work of the sieve of natural selection. 

 I therefore claim nothing new when, with the temerity of certain 

 persons treading where others are said to fear to do so, I invent 

 an inclusive term and propose to call the two fundamental factors 

 of organic evolution Plasto-diethesis 1 in which the conceptions 

 of mould and sieve are included and hyphenated. This word is 

 no more proposed for its elegance than are panmixia, amphimixis 

 and tetraplasty, though perhaps it may be the etymological 

 superior of one or more of these. It is at any rate inclusive and 

 perhaps sufficiently audacious to assure the inventor of the title 

 of Dr. Pang) oss of controversial memory. But as hard words 

 break no bones I have taken this risk and it would appear to be a 

 convenient " conceptual counter " and even Professor Karl Pearson 

 could not consistently forbid it. It has at any rate the merit of 

 having a meaning clear to all friends and opponents alike of 

 Lamarck sm. It will be observed that the two words are placed in 

 what I take to be their natural order as expressive of the Alpha 

 and Omega of the story of organic evolution. The moulding 

 process is claimed to precede that of the sieve, as physiology 

 precedes anatomy and function structure, in that form of biological 

 speculation which is held here to be the soundest. 2 



, _ , _ (YIXokttos from verb V\\<xttsiv to mould, 



xl rom til© (jrreel^. -i ^ . . 



{OiYjQStV to strain through. 



2 The twin metaphor here chosen for the name of a complex natural 

 process should be cleared a little of a certain obscurity of meaning. A mould 

 is familiar to all in domestic and industrial matters, but there are two sides 

 to the metaphorical conception. A plastic object may be moulded by the 

 hand of man as in his ruder, but more laborious days, or it may be pressed into 

 an artificial mould that he has made by means of his hands and tools. One 

 of these we know in the rude pottery made by prehistoric man and the vessel 

 of the potter described by Jeremiah the prophet. We know also those 

 machine-made moulds, so accurate as to be fitted for the coinage of a nation 



