228 



(lulaliiiif rod ol' Ophiopl. iiiuliilitlus. lii some forms Ihi- posU'iolsileral rod is 

 caiKilirulaU' to a i*ri'alc'r or k'sst-r t-xli'iil {(). roshilus. opiilcnlus). in others 

 il is composed of two closely apposed, |)arallel rods {(). tij/inis), and liiially 

 il reaches lis hiiijhesl s|)eciali/,alioii in the larva ol Ophiura Icxiurata, in 

 which il is fenestrated — another feature unique amonf> Ophiurid-larva*. 

 This characler also recalls the Kchinoid-larvae in which fenestrated rods 

 are of general occurrence: but, as was pointed out already by Metschni- 

 koff*) (com|). also ■lu'hinodermen-Larven d. Planklon-Kxp." p. 5'i) the 

 structure of the fenestiated rods of the (). U'.ilural(t-\i\v\'i\ is markedly dif- 

 ferent from that found in the Kchinoid-larva", in accordance with the fact 

 that this character has been acquired separately in the two types and is 

 a highly specializecl feature in the Ophiurid-larva?, while in the Kchinoid- 

 larvie it is, evidently, a primitive character. 



Some Ophiurid-larvK' are more or less rudimentary, showing various 

 degrees of reduction from the typical Pluteus-shaj)e to a mere worm-shape 

 which has no longer any likeness wliatever to the IMuleus-fonn. The lirst 

 stage of reduction may |)erhaps be represented by the larva of Aniphiura 

 jilifonnis. in which the |)ostcrodorsal arms have disappeared, the larva 

 otherwise being typical in shape. .\ somewhat more advanced stage of 

 reduction is probably represented by the larva of Ophiura nffinis or that 

 figured by .J oh. ]\fiiller on Taf. VII, Fig. 5 of his VI. Memoir on the 

 development of ludiinoderms. Infortnnately, only the metamorphosis- 

 stage is known, liowevei', so thai we do not know how fai' (he reduction 

 has gone; in any case the posterolateral arms are comj)lelely developed. 

 A much more reduced stage is represented by the larva figured by Melsch- 

 nikoff (Op. cil. Taf. XII. B. Fig. 15) (OphiopJuteus Melsrhnikolfi) and 

 a still further reduced stage by the larva figured by Cla pared e-) (Opiiiopl. 

 Claparedei). In these two larvae, which I have reproduced in figure 102, 

 the IMuteus-shape is, especially in the lallei-, hardly lecognizable any more; 

 the rudimentary skeleton of 0. Metschnikojfi still distinctly recalls the 

 typical Ophiopluteus-skeleton, while in (). (Aaparcdci il is reduced to a 

 pair of simple rods. In the larva re|)resented in fig. 102, ('., which was dis- 

 covered by Krohn {Opliiopliileus dumjaliis) the Pluteus-shape is no longer 

 recognizable, but traces of the larval skeleton are stated by Krohn") to be 

 found. Through these forms we reach to the larva^ of Opliiodenud hicpispiiid. 



') E. Mel sell niko n. Sliidien iilier die l-'iitwickcluiif; (I. lu'hinodeniu'ii ii. Ni'iiUTtincn 

 p. 2y. 



-) E. (Maparcdi-. lU-ohai-hUiiigen iiher Aiialoiniu u. l-jitwii-keluiigsgi'scliicliU' wirln-l- 

 loser Tiere. 186:i. Tal. I Figs. 11 12. 



') "Ini Embryo liess sich sowcilen ausser klcinorcn Kalkablageruiigun .... (Uiillii-li tin 

 gerader, starker, bis in die bciden Endcn reicliender Kalkstab unterscheiden." A. Krohn. 

 Cber eineii iieueii Enlwicklungsinodus d. Ophiuren. Miill. Arcliiv 18.')7. p. 373. 



