50 FRANK R. LILLIE. 



The only interpretation of this result is that the needle destroyed 

 a transverse section of tissue and separated the tail-rudiment from 

 the rest of the embryo, at the same time causing some injury to 

 the tissue of the tail ; secondary union then took place. The 

 tissue along the line of junction is peculiar in many respects, 

 including much material, probably remnants of cauterized parts, 

 that takes the plasma stain. 



Experiment 187. 



In this experiment the operation was made at a stage of about 

 24 hours ; the medullary plate was just formed and the primitive 

 streak was yet long ; probably 3 to 5 somites were present 

 (Fig. 9). Three spots were marked with an electrode, one behind 

 the other in the middle line towards the posterior end of the 

 primitive streak. The three spots were at first separate, but later 

 examination sho\ved them running together ; so that all of the 



- -" 



FIG. 9. Operation diagram for experiment 187 ; drawn from a blastoderm of the same 

 lot of eggs used in this experiment ; preserved at the time of the operation. 



axial structures were destroyed in this region. The embryo was 

 allowed to develop two days longer and was then preserved. 



