ECHINID^. 285 



content to hide themselves under the stones, while the species 

 having the spines slender and the shell very thin bury themselves in 

 the sand, with which they cover themselves entirely, leaving only a 

 small hole to breathe through. The species of the genus Spatangus, 

 which is furnished with short thick-set spines on the under side of 

 its body, which spread out at their extremities like the channel of 

 a spoon, proceeds with its mining operations as follows, according 

 to Mr. Jonathan Franklin : — " Figure to yourself, reader, the animal 

 on the sea-shore. He commences his operations by turning the 

 lower spines in such a manner as to form a hollow in the sand- 

 bank, in which he sinks by his own weight ; but as he sinks, a 

 great number of the spines are brought into action, throwing up the 

 sand with increased activity, while the sand thrown up, returning 

 again, soon covers the body of the worker, and it has soon buried 

 itself beneath the surface. In this situation the long hair-like spines 

 situated upon the back begin to play their part ; they prevent the 

 sand from entirely covering the animal, by forming a little round hole, 

 through which water is introduced to the mouth and respiratory 

 organs." The hiding-place of the sea-urchin is, however, easily 

 detected in the sand by the hole thus arranged for the respiration 

 of the animal, and the fishermen think they can predict storms 

 according to the depth of the hole. 



The Echinidae are reproduced by eggs, which are red and of 

 almost microscopical dimensions. As it issues from the egg the larval 

 form has the appearance of a very minute Infusorium. It is not at 

 once converted into the perfect animal, but undergoes a certain 

 metamorphosis, analogous to that of the caterpillar into the butterfly. 

 But, as Ave have already stated in treating of the Asteridae, it produces, 

 at a certain stage, by some sort of internal process of germination, a 

 sea-urchin, which, being at first only an organ of the larval form, begins 

 to live an independent life when the nursing larval form has destroyed 

 itself The manner in which the sea-urchin unfolds itself at the 

 expense of the larval form is quite analogous to that which is pre- 

 sented in the case of the Asterias, it is another case of alternate 

 generation, of which our space does not permit us to give even a 

 general outline. 



Sea-urchins are found in every sea ; they dwell in sandy bottoms, 

 and sometimes upon rocky ground. They are caught with wooden 

 pincers when in shallow water ; when found at the water's edge they 

 may be taken by a gloved hand. 



The sea-urchin, like the crab, which it also resembles in taste, 

 becomes red when boiled ; only certain species are comestible, 



