THE CAKE-URCHIN. 



727 



finest pointed needles in a fixed state, no injury could have been received from them; yet 

 their points were always struck into my hand, rapidly and severely. The natives are well 

 aware of. the offensive character of these animals, and caution the stranger against 



handling them/' 



The same author mentions that a species of Cidaris is largely eaten by the South 

 Sea Islanders, and that in various places on the sea-shore there are large heaps of its 

 shells and spines, showing that feasts have been lately held in that locality. 



CAKB-U KCHIN. Echinardctinius placenta. 



THE curiously-formed Echinus which is shown in this illustration is popularly called 

 the CAKE-UKCHIN, on account of its remarkably flattened form. It belongs to a lamily 

 which are generally called Shield-urchins, from their flat, disk-like shapes. A second figure 

 of this species is given as viewed from the side, in order to show the wonderfully flattened 

 shell, and the manner in which it rapidly slopes from the centre to the circumference. 

 The general shape and arrangement of the plates from which the shell is built may be 

 seen in the larger figure. This remarkable creature is a British species, but is not very 

 plentiful upon our coasts. The word " placenta " is Latin, signifying a flat cake, and is 

 appropriately given to this species. 



The development of the Echinus is so very remarkable, that it deserves a passing 

 notice. This creature passes through a metamorphosis even more strange than that of 

 the insect, and no one who was not acquainted with the animal could possibly recognise 

 in the delicate framework of translucent spines the larval form of the globular Sea- 

 urchin. At first, the little creatures are almost shapeless and globular, rolling about 

 through the water in an uncertain kind of way. But by degrees they put forth a dome- 

 like portion, from which proceed several slender calcareous rods, altogether making a 

 figure that has been aptly compared to a skeleton French clock. In this state it was 

 formerly known by the name of Pluteus. As if to carry out the comparison still further, 

 the first indication of change to its more perfect form is the development of a circular 



