200 



INTERNAL FACTORS 



IV. i 



in the isolated blastomeres, their subsequent development is pro- 

 gressively retarded as the germinal value decreases (Table XXI). 



TABLE XXI 



Showing the rate of development in partial larvae. 

 Germinal value. 



FIG. 111. Sphaerechinits Plutei, showing the gut. a }, b. J, c. j. 

 (After Driesch, 1900.) 



It is evident from these experiments that, in the Echinoderms, 

 while the isolated parts of the egg, whether blastomeres or egg- 

 fragments, are only able to segment as they would have done 

 had they remained in connexion with the whole, they are never- 



