46 HENRY BURY. 
hypothesis) they exhibit a primitive approach to a worm-like 
ancestor. 
With a view to clearing up some of these differences of 
observation and opinion, I commenced in the spring of 1888 
an examination of the metamorphosis of all available Echino- 
derm larve, paying special attention to the behaviour of the 
mesentery, in the belief that this would afford an important 
clue to the difficult question of the origin of Echinoderms and 
the relation of the radiate adult to the bilateral larva. 
The solution of so wide a phylogenetic question cannot be 
hoped for, and should not be attempted as often as it is, from 
the narrow standpoint of the ontogeny of one or two forms; 
nor should too much reliance be placed upon the accounts of 
other observers, however careful they may be, whose attention 
has not specially been directed to the points at issue. As far 
as possible, therefore, I have worked out for myself the meta- 
morphic changes of at least one form of larva in each of the 
five classes of Echinoderms. 
I very soon found, however, that to understand these changes 
properly it was necessary to go back in almost every case to 
much earlier stages—in some cases right back to the earliest 
formation of the body-cavities from the archenteron. It would 
have been most undesirable to burden the pages of the present 
paper with the preliminary results thus obtained; and I there- 
fore in 1888 (5) published an introductory paper on the sub- 
division of the enteroccel and the origin of the skeleton, which 
I intended to follow up as soon as possible with the present 
paper on the metamorphosis and phylogeny; but ill-health 
altogether stopped my work for a long period, and even now 
the difficulty of obtaining material has prevented me from 
carrying out my scheme as fully as I had hoped. It did not 
seem desirable, however, to withhold any longer the numerous 
facts bearing on the subject embodied in the subsequent pages. 
Most of the material for these studies was obtained at the 
Zoological Station at Naples in the spring of 1888, but a second 
visit there in 1893 was necessary to complete my studies of 
Auricularia ; while for most of my larve of Asterias rubens 
