72 



MARINE ANIMALS. 



ECHINODERMATA, {THE ECHINUS) 



BY 0. S. ROUND, ESQ. 



A, Exterior view of Echinus Miliaria, natural size. B, A section of the same, shewing the lantern and 



teeth C. 1), Interior of a piece of shell of Echinus, shewing; tlie perforations throuj,'h which the 



Suckers work. 



This genus of Marine Animals, with the shells of which almost every 

 one is familiar, is the Echinus, or Sea-urchin* so called from the universal 

 presence of spines, in more or less proportion of production over the whole 

 surface of the shell. This shell is composed of five pieces, that is by per- 

 ceptible sutures, but to give the number of actual plates of which it is 

 composed, would be an almost impossible, probably a most fruitless task. They 

 are certainly, ordinarily speaking, several hundreds in number, and exhibit in 

 the progressive growth of the creature the most wonderful arrangement. The 

 shape we know is a flattened, although somewhat irregular sphere, inasmuch as 

 where the larger orifice exists, which is, in fact, the mouth, the arch is 

 suddenly contracted, but this figure is found to be composed, upon close 

 examination, of an infinite number of pieces of calcarious matter, differing, 

 or rather increasing or decreasing in size as the shape of the shell enlarges 

 or lessens^ and hence at the largest part the plates will be largest. Between 

 each of these plates, the substance, of which the animal itself consists, is 

 protruded, and this substance is constantly collecting around the edges of these 

 plates, earthy and calcarious matter, which being added on, as it were, in 

 regular progression over the whole shell, this covering regularly increases in 

 size with the growth of the inhabitant, without in the smallest degree losing 

 its elegant shape and beautiful appearance; ornamented and embossed as it is 

 with patterns like the most beautiful artificial raised work, incomparable, 

 however of course, with any human productions. 



In many of the species, particularly those in common collections, known as 

 sea-eggs, and which are the skeletons of the Echinus, the spines are so 

 minute as to be hardly discernible between the plates; in some attaining 

 several inches in length, and of a proportionate thickness; whilst in others, 

 the resemblance to the common urchin, or hedgehog is very striking; and in one 



