REGENERATION 181 



the early history of the embryo that it usually 

 consisted of elements derived from two parents 

 of different sexes; that the originally single 

 cell divided into two; that each of these again 

 divided, and so on. The result of these con- 

 tinued divisions is to convert the originally 

 single cell into a mass of cells all derived from 

 it. This solid mass of cells suggested the ap- 

 pearance of a mulberry to its first describers 

 and consequently received the name of Morula. 

 Then by processes which cannot be detailed 

 here, this solid mass becomes a hollow sac 

 which we may think of as being very like a 

 raspberry when we have pulled away its stalk 

 and the uneatable part that goes with it, and 

 if we imagine the hollow spheroid closed into 

 a ball at the hole left by their removal. At 

 this stage it is called a Blastula, and we need 

 not follow it further, except to say that in 

 higher forms differentiation sets in so that the 

 different organs of the adult body are developed 

 from what was once an indifferent mass of cells. 

 It will be remembered that it was shown 

 to be possible to shake apart the cells of the 

 developing morula of Amphioxus so that in 

 place of the single individual which they would 

 normally have formed, a collection of say 

 oight will be formed. To put it in another way 

 each of these first eight cells (it may be more, 



