106 VITALISM AND SCHOLASTICISM 



arrives at the haven for which it set out with- 

 out being deterred by the difficulties put in its 

 way. A number of experiments of this kind 

 have been made and will be found in books 

 dealing with questions of this kind. One or 

 two of them may here be described in as simple 

 language as possible, so that the reader un- 

 versed in biological literature may be able to 

 understand something of the weight of evi- 

 dence which lies behind the argument now 

 under consideration. 



First of all then we may consider certain 

 Frogs and experiments in the modification of the develop- 

 18 ment of the eggs of frogs and sea-urchins, for 

 both behave alike under these circumstances. 

 The course of segmentation in these cases is as 

 well known as the route from London to 

 Brighton and the first result of segmentation 

 is the production of a sphere of cells from which 

 the later organism takes its form. Now the 

 process of this development has been modified 

 by placing the egg between plates of glass so 

 that it must develop under pressure. As 

 a result of this pressure it becomes impossible 

 for the rapidly increasing number of cells to 

 arrange themselves in a sphere as they would 

 naturally have done, and they are forced to 

 develop in a plane between the two sheets of 

 glass. If the process were to be carried on 



