344 EVENINGS AT THE MICROSCOPE 



of the points of the visor to one of the ear- points. Herr 

 Miiller compares the larva (which is not helmet- shaped in 

 every species) to a clock-case, of which the visor, with its 

 hanging gullet and mouth, forms the pendulum, and then 

 the newly- formed disk represents the face of the clock, 

 only it is put on the side instead of the front. Now this 

 tiny disk gradually grows into the form and assumes all 

 the organs of the Urchin, while the enveloping nurse, 

 flesh, rods, and all, wastes away to nothing. 



The. disk, soon after its appearance, is seen to bear 

 prominences on its surface, in which is traced the figure 

 of a cinque-foil, the elements being five warts set sym- 

 metrically. These lengthen and grow into suckers, essen- 

 tially identical with those of the adult, but most dispro- 

 portionately large. In the five triangular interspaces 

 between these, little points and needles of solid calcare- 

 ous glass begin to form, very much like the crystals that 

 shoot across a drying drop of a solution of some salt; 

 these catch and unite, first into "f, and then into 

 |-| forms, and then into irregular networks. Meanwhile, 

 fleshy cylindrical columns spring up from the surface, one 

 in each of these interspaces, and presently develop, within 

 their substance, a similar framework of porous glass; 

 these soon manifest themselves to be the spines, and each 

 is seated on a little nucleus of network, on which it pos- 

 sesses the power of rotating. 



At the same time pedicellarias begin to be formed; 

 and, what is specially marvellous, they are first seen, not 

 on the disk, which alone is to be the future Urchin, but 

 on the interior wall of the helmet, which is even now in 

 process of being dissipated, and even on the opposite side 

 to that which carries the disk. They commonly appear 



