THE METAMORPHOSIS OF ECHINODERMS, 45 
The Metamorphosis of Echinoderms. 
By 
Henry Bury, ™.A., F.L.S., 
Late Fellow of Trinity College, Cambridge. 
With Plates 3—9. 
INTRODUCTION. 
Acassiz’s view, put forward more than thirty years ago 
(1, p. 61), that the actinal and abactinal surfaces of Echino- 
derms (at least of Echinids, Asterids, and Ophiurids) are 
formed from the right and left enteroccel pouches (‘ water- 
tubes,” as he calls them) respectively, has met with very 
general acceptance ; but surprisingly little has been done to test 
it by modern methods. 
Agassiz’s observations were, of course, made on the whole 
larvee, without any assistance from sections. Gd6tte (9) in 
1876 applied the section method to Antedon, and found 
Agassiz’s view to hold good there; yet, on the other hand, 
Ludwig (15) in 1882 failed altogether to trace this symmetrical 
arrangement of the enteroccls in Asterina, while he showed 
conclusively that Agassiz was mistaken in supposing that 
the left enteroccel gives rise to nothing but the hydroccel. 
No one has ever attempted, so far as I know, to show how 
Holothurians can be included in Agassiz’s scheme; and the 
conclusion of those who have studied their development has 
generally been (21, 31, 32) that in retaining the dorsal mesen- 
tery of the larva as a longitudinal mesentery in the adult (not 
a transverse one, as it isin Antedon, and should be on Agassiz’s 
