2l8 J. S. HUXLEY. 



After 24 hours all had become somewhat reduced in size, with 

 slightly denser appearance. The gut too was shrunken. The 

 arms, especially the third pair, usually showed slight reduction in 

 size. 



After 48 hours, marked changes had occurred (Fig. 7). The 

 third pair of arms had in all cases totally disappeared, and the 

 others showed considerable but variable resorption. The prev- 

 iously noted swelling of the trunk and aboral region was present 

 to a greater or less decree. The most interesting change was 

 seen in the gut, which was always contracted, and contained a 

 greater or less number of small round bodies. On examination 

 with a higher power, these proved to be cells, practically spherical, 

 and not cohering. They had presumably migrated out of the 

 stomach epithelium into the lumen. 



This is paralleled by the migration of the cells out of the aboral 

 ectoderm in Expt. C above (pp. 212-213), and by the behavior of 

 the tissues in organisms that dedifferentiate by resorption, as in 

 Pcrophora (Huxley, '21 &) and Hydroids. (Loeb, 'oo. Huxley 

 and de Beer, in press.) 



After 72 hours, dedifferentiation had progressed much further 

 (Figs. 8, a and b). The size is much less, the arms very small 

 and extremely dense, the gut quite packed with cells, and much 

 contracted. The contraction of the gut has expelled some of the 

 cells at the anus and sometimes also at the mouth. The trunk 

 and aboral regions are sometimes swollen, more usually con- 

 tracted. A fair number of plutei had died. 



At this stage the survivors were replaced in sea-water. 



KCN. Experiments on 4-day plutei in KCN 11/100,000 and 

 n/2OO,ooo gave on the whole similar results to those in HgCl, 

 11/1, 000,000. Disintegration of the trunk ectoderm was never ob- 

 served, and is possibly a specific effect of Hg (rf. Child, '17). 

 Arm-resorption was not quite so rapid. 



4. EXPERIMENTS ON RECOVERY. 



These are very incomplete, owing to lack of material. Through 

 the courtesy of Mr. J. Gray, who independently observed dedil- 

 ferentiation phenomena, in larvse treated with citrates, I am 

 enabled to state that in this case some degree of recovery at least is 

 possible. It would here appear that forms which have resorbed 



