350 



EVENINGS AT THE MICKOSCOPE. 



The difck is meariAvliile enlarging its area; and the 

 spines and suckers, gradually lengthening, at length 

 push themselves through the walls of the helmet ; the 

 hanging points and crest of which are fast diminishing 

 hy a kind of insensible absorj^tion ; the ciliary move- 

 ments become less vigorous, and the mouth closes up. 

 But, correspondentlv, the Urchin is beginning to ac- 

 quire its own independent 

 power of locomotion ; for the 

 suckers, now ever sprawling 

 about, are capable of adhering 

 to any foreign body with 

 which they come into contact, 

 and of dragging the whole 

 structure about, by their prop- 

 er contractions. The cilia 

 that cover the thickened fring- 

 ing band still exercise their 



YOUNG sea-urchin; , , - 



Deveiopmevt of Disk. powcrs, and are the last to 

 disa])pear. 



When the disk has grown to such an extent as to 

 spread over about half of the larval stomach, very 

 little remains of the helmet, except the middle portions 

 of the glassy rods and the ciliary bands ; all the rest 

 of this exquisitely modelled framework having van- 

 ished by insensible degrees, no one knows how or 

 where. The stomach and gullet indeed are gradually 

 sucked into the cvei'-growing disk ; but all the rest, 

 flesh and rods, fringes, bands, and cilia, waste away to 

 nothing. 



The mouth of the larva has no connexion with the 

 mouth of the Urchin. The little isolated patches of 

 glassy network continue to spread through the flesh 



