THE DEVELOPMENT OF ASTERINA GIBBOSA. 355 
the action of their general covering of cilia, and they had no 
power of re-attachment. In the case, however, of larve which 
were attached by what we may call voluntary muscular action, 
if one brought the pipette cautiously near so as not to alarm 
them, it was very easy to remove them from a stone, just as it 
is easy to kick a limpet off a stone if it is taken unawares; 
but if they were irritated they were excessively difficult to re- 
move, and when one finally succeeded in getting them up into 
the pipette, unless one promptly re-expelled them, they at- 
tached themselves to the glass, and it was almost impossible to 
detach them from it. 
The metamorphosis of Echinoderms is probably the most 
remarkable ontogenetic change known in the animal king- 
dom; but our knowledge of its details has been up to the 
present most insufficient. We possess a completely satis- 
factory account of only one form, viz. Antedon, for which the 
credit is due to the researches of Bury (1), which have been 
amply confirmed by Seeliger (18). As I mentioned in the 
introduction, I hope the account I am about to give of the 
metamorphosis of Asterina will compare in completeness with 
those I have just mentioned; and as it is of the utmost im- 
portance for the comprehension of the meaning of the anato- 
mical structure of the Asterid that its relation to the larva 
should be thoroughly grasped, I shall anticipate a little what 
I have to say in order to make the essence of the process per- 
fectly clear. The metamorphosis of the Asterid, then, consists 
in the following processes, which go on simultaneously : 
(1) The constriction of the body into disc or body sensu 
stricto, and stalk, the latter being formed from the preoral 
lobe. 
(2) The sharp flexure of the disc on the stalk [the former is 
bent obliquely downwards and to the left. This is not well 
shown in any of the figures copied from Ludwig ; it is better 
seen in the diagram, Pl. 29, fig. 158 (Dec. 1895) ]. 
(3) The preponderating growth of the organs of the left side, 
the left posterior celom and the left hydroccele both sending 
out dorsal and ventral horns, which meet so as to form complete 
VoL. 38, PART 3.—NEW SER. AA 
