444 On the Metamorphosis of the Ophiuridge and Ecliinidse. 



One of these larvae was once seen in which the axis of the 

 larva had almost entirely disappeared^ and in which no further 

 trace of the oral framework remained. The young Echinus formed 

 an elongated^ spherical, somewhat flattened body without a trace 

 of any Echinoid arms, and in which one half of the surface was 

 completely covered with spines, but the other half was still cu- 

 taneous and exhibited traces of the integument of the dome of 

 the larva. For in addition to the pigment spots, several irregular 

 remains of the innermost concealed part of the column and its 

 branches in the dome were visible. The spinous side was convex 

 like a watch-glass, but elongated, and here and there exhibited am- 

 bulacral pores, and at the circumference some very large tentacles 

 or feet projected, the distribution of which I could not clearly 

 ascertain. No mouth is visible at the opposite cutaneous portion 

 of the flattened sphere. This may possibly exist at one extremity 

 of the elongated body, but it was impossible to determine this 

 from the opake structure of the body. The length and form 

 of the spines are the same as in the above. 



On one occasion an exactly similar body, of equal size, spinous 

 upon one half, elongated, spherical and somewhat flattened (one- 

 fifth of a line long), and free from all larval remains, was observed. 

 Like the previous one it was obtained near the surface of the sea, 

 but it moved upon the glass exactly like an Echinus, putting the 

 spines separately into action, and at the circumference extending 

 some large tentacles, by which it held on to the glass. The centre 

 of the spinous surface was free from spines. I recognised a 

 surface divided into five parts and with a pentagonal centre, 

 through the skin spotted with pigment which exists at this part. 

 The side opposed to the spinous half was convex, but still covered 

 merely by the spotted integument, beneath which, remains of the 

 calcareous axes of the larva were still visible. Neither on this 

 occasion was any certain information obtained regarding the 

 mouth, and it remains doubtful whether it existed at either ex- 

 tremity of the elongated, round body. The question is, whether 

 the entire series of developmental phsenomena just described be- 

 longs to an Echinus or rather Spatangus. Although the ultimate 

 forms of the larvae which have been examined are so difierent, 

 nevertheless it is remarkable that the larvae of the Ophiurce and 

 Echini agree in being formed upon a certain common plan. The 

 larvae of the Asterice observed by Sars differ most, but these also 

 agree with the common plan in their bilateral appendages ; hence 

 it may be supposed that an analogous starting-point may be 

 found for all the Echinodermata. For this purpose, however, 

 it will be necessary to re-examine the larvae of the Asteria. Their 

 internal structure and the position of their mouth are entirely 

 unknown ; moreover I have not succeeded in observing from the 



