156 Edwin G. Cojjklin. 



It therefore seemed possible that the production of a complete 

 larva from any one or two of the first tour cells might be due to the 

 replacing of a missing substance by the greater development of 

 the trace of that substance contained in the cells in question. Thus 

 the anterior quadrants which lack the yellow crescent might, 

 perhaps, regenerate it from the small amount of yellow perinuclear 

 protoplasm which they contain, and correspondingly the posterior 

 quadrants might regenerate the lacking gray crescent from the 

 small amount of gray substance which they contain. In the light 

 of the work of Driesch and Crampton either there must be such 

 regeneration, or the substances which appear so different must 

 after all be each and all totipotent. 



However the solution of this problem has turned out to be much 

 simpler than I had supposed possible, viz: isolated blastomeres do 

 not give rise to entire larvce, as claimed by Driesch and Crampton, 

 but on the contrary each blastomere produces only those parts of a 

 larva which would arise from it under normal conditions. The 

 development is, in short, a " mosaic work." Since the first cleavage 

 is bilaterally symmetrical each of the first two blastomeres con- 

 tains one-half of each and all of the substances of the egg and 

 correspondingly the half larva which develops from one of these 

 blastomeres contains portions of every larval organ. Owing to 

 the fact that the cells which arise from an isolated blastomere 

 close over the injured surface these partial embryos are rounded 

 in form and many of the one-half larvae resemble superficially 

 whole larvae of half size, but in no case are they complete. When 

 the anterior or posterior quadrants of the 4-cell stage are killed 

 nothing even remotely resembling a normal larva is ever pro- 

 duced. My results are therefore directly opposed to those of 

 Driesch and they agree in all essential respects with those of 

 Chabry. 



The partial embryos and larvae obtained in these experiments 

 may be classified as right or left, anterior or posterior, dorsal or 

 ventral, or composite forms. Furthermore they may be known 

 as half, quarter, eighth, sixteenth, etc., embryos, according as 

 they are produced from blastomeres of the 2, 4, 8, 16, etc., cell 

 stages; however, the character of the embryo depends entirely 

 upon the region from which the isolated blastomeres come and 

 not upon the number of such blastomeres. 



