63 



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

 Strongylocentrotus pulcherrimus and Heliocidaris tuberculata, take a com- 

 paratively long time to develop; but, as stated above, it is hardly justifi- 

 able to conclude that 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 the body and arms. — The body-skeleton (Fig. 23) forms 

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

 rod not having united with 

 the body rod; but since I 

 have noticed after observation 

 on the living specimens that 

 "the body skeleton is like that 

 of Heliocidaris tuberculata" 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 fig. B. 

 In some of the specimens with 

 the skeleton preserved the 



body skeleton is considerably Fig. 23. skeleton of the larva of Evechinus chloroticus, 

 more complicate than in the 1st stage. SUghtly abnormal, ^as/^. a. front view; 

 », 1 • 1 T-i- rio B. side view. Letters as in flg. 20. 



specimens after which Fig. 23 



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

 Heliocidaris tuberculata 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 B there is seen an indication of a double recur- 

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

 fenestrated; in the specimens where the skeleton is preserved it shows 

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

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

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

 that the postoral rod 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 dorfeal side the 

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



