96 EMBRYOLOGY 



We are asking the same question: Are the parts all determined in detail ? We 

 have the same problem of an apparently homogeneous system developing 

 into a very complex structure. In the sea urchin egg we were dealing with an 

 apparently homogeneous egg developing into a complicated larva. In the 

 self-differentiation of any organ — the limb, for example — we again meet 

 this same problem of a mass of homogeneous-appearing cells developing 

 into a complicated structure, a highly organized structure. 



In the next chapter we shall consider experiments which illustrate the kind 

 of organization which the individual structures — limb, ear, etc. — possess in 

 the neurula stage. 



