REPRODUCTION 65 



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 unversed in biological literature 

 may be able to understand something of the weight 

 of evidence which lies behind the argument now 

 under consideration. 



First of all then we may consider certain ex- 

 periments in the modification of the development 

 of the eggs of frogs and sea-urchins, for both be- Frogs and 

 have alike under these circumstances. The course 9ea " ul 

 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 became impossible for 

 the rapidly increasing number of cells to arrange 

 themselves in a sphere as they would naturally 

 have done, and they were forced to develop in a 

 plane between the two sheets of glass. If the 

 process were to be carried on too long the result 

 would be the death of the developing creature from 

 sheer want of room, so it must be released after 



the experiment has gone a certain distance. What 



B 



