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REGENERA TION 



nection with the experiments on the sea-urchin's eggs. Later I ('96) 

 also obtained whole larvae from one-half and one-fourth blastomeres, 

 and I also found that the one-eighth blastomeres do not develop 

 beyond the blastula stage. The number of cells of which the one- 

 half larva is composed is half that of the normal larva, and the one- 



FlG. 66. Ctenophore-egg and embryo. A. Normal sixteen-cell stage. B. Half-sixteen-cell 

 stage. C. Later half-segmentation stage. D. Later half-embryo. E. Corresponding whole 

 embryo. F. Half-embryo seen from side. G. Same seen from apical end. In F and (/, 

 four rows of paddles present, three endodermal sacs and ectodermal stomach. 



fourth larva is made up of one-fourth of the total number of cells. 

 In all the preceding cases in which the blastomeres have been sepa- 

 rated, a whole embryo has developed, although the cleavage was 

 often like that of a part. In one form, however, it has been found 

 that a whole embryo does not develop. Chun ('92) first showed that 

 the isolated one-half blastomere of the ctenophore egg produced a 



