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C. M. Child. 



retard or prevent the decrease in width in this part ot the body to 

 a certain extent, hence the unusual width even in late stages 

 (Fig. 10) of the posterior part of the old tissue. This, ot course, 

 determines the width of the new tissue at the level ot the boundar\- 

 between old and new. Consequently this also is wider than usual 

 (compare Fig. 10 with Fig. 4). 



This piece was accidentally killed at the stage of Fig. 10. 



Series j8 (Figs. 11-16). In this series a specimen somewhat 

 smaller than the preceding was cut transversely near the posterior 

 end of the phannx (Fig. 11). Figs. 12-16 show the changes in 

 proportion which occurred, Fig. 14 is probably not quite fully 

 extended. The decrease in width at the posterior end ot the old 

 part is marked in Figs. 12-14. Toward the end of the experiment 

 (Figs. 15-16) the change is an almost proportional reduction in 

 size, though with approaching exhaustion there is some relative 



