DEDIFFERENTIATION IN ECHINUS LARV/E. 237 



FIGS. 6-8, AND 14. g-day plutei in HgCU n/i, 000,000. 



FIG. 7. After 48 hours, in n/i, 000,000 HgCl 2 . The third pair of arms 

 has disappeared, the other arms markedly reduced ; note the clubbing of one 

 of the anal arms. The stomach contatins numerous cells migrated out of its 

 walls. Aboral and trunk regions are swollen. Lateral view. 



FIG. 8. After 72 hours in n/i, 000,000 HgCl 2 . 



FIG. 8a. The arms are markedly dense, and very small. The skeleton of 

 the oral arms protrude slightly. The remains of the oral lobe are visible. 

 Stomach and oesophagus are quite dense. Cells have been extruded from 

 both anus and mouth. The trunk is slightly swollen. Lateral view. 



FIG. 8&. More advanced stage. The oral lobe has disappeared, the arms 

 are dense and shorter, the trunk and aboral regions are affected. Cells 

 have been extruded at the anus. Lateral view. 



FIG. 9. Wide-angled pluteus. 2 days from fertilization in KCN n/ 100,000. 

 2 days in sea-water. Only the anal skeleton is drawn. Anal view. 



