THE DEVELOPMENT OF PATTERN 99 



by experiments. It is not supposed to have any con- 

 nection with the religious or moral soul, but it is a 

 sort of developmental soul. A hypothesis like this is 

 in the first place a confession that we do not under- 

 stand how the harmony of development is brought 

 about, but more than that, it denies that we shall 

 ever find out. It is frankly defeatist, and on those 

 grounds alone it is usually discounted by scientists 

 at the present day, who feel that, although they do 

 not understand all about development yet, they 

 still have no grounds for saying that they never will 

 understand it in the future. Moreover, the organizers 

 have an easier job than the pointsman in a shunting 

 yard, because in any one kind of embryo the final 

 state is fixed. It is as though there was always the 

 same set of trains to be made up in the final sidings. 

 The organizers have only to deal with variations in 

 the raw material, while the pointsman has as well 

 to build up different sets of trains on different days. 

 The living newt organization centre therefore does 

 two things, it evocates a neural plate from the 

 gastrula ectoderm, and then it individuates itself and 

 the neural plate and its surroundings generally into 

 a complete embryo, or as big a part of one as pos- 

 sible. And we can separate these two processes by 

 using dead organizers, which evocate but do not 

 individuate. Some of the other organization centres 

 we know of seem only to individuate. This is so 

 with the sea-urchin centre discovered by Horstadius ; 

 wherever the small vegetative cells are placed they 

 try to build up a whole embryo. Perhaps Seidel's 



