THE DEVELOPMENT OE ASTBRINA GIBBOSA. 237 



the action of their general covering of cilia, and they had no 

 power of re-attachment. In the case, however, of larvEe 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 diiRcult 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 prseoral 

 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, PI. XXII, fig. 158 (Dec, 1895) ]. 



(3) The preponderating growth of the organs of the left side, 

 the left posterior coelom and the left hydroccele both sending 

 out dorsal and ventral horns, which meet so as to form complete 



VOL. 6. ^ 



