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. 



CAKE-VRCttlN.-Echlaarachnlus placenta. 



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

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

 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 wonder- 

 fully flattened shell, and the manner in which it rapidly slopes from the centre of 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 

 recognize 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 



