186 



ECHINODEKMATA. 



the individuals belonging to that family undergo a series of changes 

 that are truly surprising in their character. 



(488.) The young Ophiura on leaving the egg presents itself under 

 a most grotesque form, in which condition it has been long known to 

 naturalists, and described under the name of Pluteus, or Easel Animal- 

 cule, from its resemblance to a painter's easel. 



(489.) The Pluteus paradoxus (fig. 92) is exceedingly minute, being 

 not more than fths of a line in length. When highly magnified, its 



Fig. 92. 



1. Pluteus paradoxus. A A, lateral arms ; B B, inferior ditto ; C C, anterior ditto ; D D, posterior 

 ditto ; a, mouth ; a', resophagus ; 6, stomach ; c, granular bodies, the nature of which is uncertain ; 

 d, cfficiform appendages, which make their appearance around the oesophagus and stomach, and 

 which are the first indications of the development of the Star-fish ; e, ciliated bands ; f, calcareous 

 framework of the skeleton; g, zone of cilia surrounding the apex of the body; a; nervous system. 

 2. Further development of the caeciform appendages, d ; they begin to exhibit the appearance of 

 the body or central disk of an Ophiura. (After Miiller.) 



body is seen to be somewhat of a conical shape, terminating above in a 

 point, but dividing inferiorly into eight long processes or appendages 

 of various dimensions, to which it owes its peculiar figure (fig. 92, l, 

 A, B, c, D). Each of these processes is supported by an internal cal- 

 careous framework derived from the interior of the body (fig. 92, I,/), 

 which, branching out in different directions, forms a basis whereon the 

 soft parts are spread out. The whole animal is perfectly transparent, 

 its substance resembling dull glass, the apex of the body and the ex- 

 tremities of the arms or processes being slightly tinged with orange. 



(490.) These singularly -formed larvce for such they are are found 

 abundantly during the months of August and September, crowding the 

 surface of the sea in rich profusion, swimming freely about by the aid of 

 rows of cilia (e), with which their arms and the apex of their bodies (g) 

 are plentifully furnished. They possess, moreover, a distinct nervous 

 system, consisting of two little ganglia (#) situated just beneath the oral 

 aperture, from whence delicate nervous threads may be traced in dif- 

 ferent directions. 



