63 



H 



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

 Strongylocentrotus piilclierrinnix and lldiocidaria lubi-irnlnltt, take a com- 

 paratively long lime lo develop; hut, as stated ahove, 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 I In- point of the arms, only few scattered 

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

 a basket structure; in the figure A Ihe 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 thai 

 "the body skeleton is like thai 

 of Heliocidaris tuberculata" it 

 can hardly be doubled thai 

 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 Ihe 

 body skeleton is considerably 

 more complicate than in Ihe 

 specimens after which Fig. 23 

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

 lleliocidarif; liibeirulalu and Echinonuini luciinler (Figs. 21. 25). It is im- 

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

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

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

 complicate body skeleton similar lo lhal occurring in the two forms 

 mentioned; in the Fig. 23 15 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 Ihe skeleton is preserved it shows 

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

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

 tain lhal lliis rod is normally thus constructed it is only safe to say 

 lhat the posloral rod is fencslralcd. The anlerolateral 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 



Fig. 2.'i. Skeleton of Ihe larva of /'CCC/I/'/K/.S fhlomlicux. 



1st stage. Slightly abnormal. -- 5 ,. A. front \ie\v: 



H. side view. Letters as in tig. 2(1. 



