SEA-URCHINS AND SEA-CUCUMBERS. 349 



represents tlie 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, 

 waste away to nothing. 



The disk, soon afte]*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. Tliese lengthen and grow into suckers, es- 

 sentially identical with those of the adult, but most 

 disproportionately large. In the five triangular inter- 

 spaces between these, little points and needles of solid 

 calcareous glass begin to form, very much like the crys- 

 tals that shoot across a drying drop of a soluton of 

 some salt; these catch and unite, first into -"J", 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 pres- 

 ently develop, within their substance, a similar frame- 

 work of porous glass ; these soon manifest themselves 

 to be the spines, and each is seated on a little nucleus 

 of network, on which it possesses the power of rotating. 



At the same time pedicellarise 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 four in number, arranged in 

 two pairs ; and one can see in them — they being, like 

 the suckers, large out of all proportion to the disk — 

 the stem, and the three-leaved heads, which already 

 exercise their characteristic snapping movements. 



