63 



is five weeks old. This larva is, accordingly, among those which, like e. g. 

 Slromjyloreiitroliis pulclwrrinnis and Ileliocidaris luberrulala, lake a com- 

 paratively long lime lo develop; bnt, as stated above, it is hardly justifi- 

 able to conclude I ha I the development normally proceeds quite so slowly. 

 In the young Pluteus stage (PI. X, Fig. 1) the body is short, in accordance 

 with the character of the body skeleton. There is a very distinct suboral 

 cavity. No pigment spots in the point of the arms, only few scattered 

 pigment cells in liie body and arms. — The body-skeleton (Fig. 23) forms 

 a basket slrueluio; in the figure A the frame is not complete, the recurrent 

 rod not having united with 

 the body rod; but since 1 jj^\ 



have noticed after observation 

 on the living specimens that 

 "the body skeleton is like that 

 of Heliucidaiis liibeirulata' it 

 can hardly be doubted that 

 normally the recurrent rod 

 unites with the body rod to 

 form a complete basket struc- 

 ture as it does also in tig. B. 

 In some of the specimens with 

 the skeleton preserved the 



body skeleton is considerably Fig. 23. skeleton of the larva of /•:wr7i/;i(i,scWoro/icus, 

 more complicate than in the '^t stage. Slightly abnormal. -«/,. a. from view: 

 „. ... „. „,, B. side view. Letters as in fig. 20. 



specimens after which big. 23 



was drawn, looking more or less distinctly like the structure found in 

 Heliocidaris luberculala and Echinometra lucunter (Figs. 24, 25). It is im- 

 possible to ascertain from this material what is really the normal struc- 

 ture of the body skeleton in this larva, but, in any case, it is important 

 to notice that there is a distinct tendency in this larva towards forming a 

 complicate body skeleton similar to that occurring in the two forms 

 mentioned; in the Fig. 23 H there is seen an indication of a double recur- 

 rent rod. The body rod is rather coarsely thorny. The postoral rod is 

 fenestrated: in I lie specimens wliere the skeleton is preserved it shows 

 more or less pronounced abnormalities. It is seen to consist only of two 

 component rods in the outei' part; I would, however, not venture to ascer- 

 tain that this rod is normally thus constructed — it is only safe to say 

 that the ])ostoral lod is fenestrated. The anterolateral rod is almost smooth. 

 The fully formed larva (PI. X, Fig. 3) has two pairs of vibratile lobes 

 and short, earshaped postero-lateral processes. On the dorsal side the 

 vibratile band forms a pair of lobes, supporting a raised wall across the 



