130 



Organisms from Eggs 



zones can be recognized in the egg (Fig. 9), a small clear 

 cap A at one pole, a pigmented ring B, and the 



rest again un- 

 pigmented C. 

 Observation 

 has shown that 

 each one of 

 these regions 

 gives rise to a 

 definite con- 

 stituent of 

 the egg: A fur- 

 nishes the 

 mesenchyme 



FIG. 9 ; 



from which the 

 skeleton and 

 the connective tissue originate; B is the material for 

 the formation of the intestine, and C gives rise to the 

 ectoderm. 



The pigment is only at the surface of the egg, and its 

 collection at B indicates only that the material in B 

 differs physicochemically from A and C. The real 

 determiners of the three different groups of organs are 

 three different groups of substances whose distribution 

 is approximately but probably not wholly identical 

 with the regions indicated by distribution of pigment. 

 The intestine-forming material is probably not entirely 

 lacking in C but is contained here in a lower concen- 



