234 



which appears to be a structure characteristic of Auriculariae and Ophio- 

 phitei. It was discovered by Metschnikoff and made Ihe object of a 

 closer study especially by Senion in his pajjcr on "Die l^ntwicl<elung der 

 Synapta digitala"'); furtlierniore Chun described the nervous system of 

 Auriciilariti niKlibranchiata, while it was observed by myself in Auriculariu 

 (mlarclica, ;dl tlusf loinis agreeing very closely in regard to the shape 

 and position of this structure. Quite recently MacBride, (Echinoderm 

 larva:" of the British Antarctic ("Terra Nova") Expedition) gives a repre- 

 sentation of the nervous system of Auricularia antarclica (PI. I, Mgs. 1 — 2) 

 quite dillerent from that given by me (Echinodermen-Larven d. deutschen 

 Siidpolar Expedition p.81,Taf.X, Fig. 1 ;Taf. XI, Fig.2). There is, however, 

 hardly any doubt lluil what MacBride here represents as the larval ner- 

 vous system is the edge of the atrium, which continues some way on to 

 the oral area as a streak of thickened skin (comp. my memoir quoted 

 above, p. 79, Taf. IX, Vig. 1), such as it was also found by Chun in Auri- 

 cularia luulibranchiald. 1 do not want to deny the possibility that this 

 structure may be of a iili nous character, but that has not yet been proved, 

 and. in any case, it is not the homologue of the nervous system of Auri- 

 cularias in general: this latter structure is found more laterally in the oral 

 area and is not in direct connection with the mouth-). 



In the Ophiurid-larva; the nervous system is essentially like that of the 

 Auricularia, forming a band across the oral area to each side of the mouth; 

 for a more detailed representation of this structure in Ophiurid-larvge I 

 may refer to my paper, "Notes on the development of some Scandinavian 

 Echinoderms" p. 158 — 160. — In Echinoid-larvae the nervous system is 



') Jen. Zc'itsc-lir. f. Naturwiss. XXII. 



*) I may lake the opporluiiity here lo object to a statement by MacBride concerning 

 my representation of the coelomic structures of Auricularia antarclica. On describing the stage 

 represented in his Fig. 2 MacBride says (Op. cit. p. 87) that "this stage corresponds witli 

 tliat represented in text-fig. 1 in .>Iortensen's latest jiaper, but .M. has ((uitc misunderstood it. 

 He o^•erlooi<ed the rudiment of the posterior coeloni altogetlier, and lias ligured a sac entirely 

 detached from the anterior coelom as the posterior enterocoele. This sac, whicli lies above the 

 junction of the stomach and intestine, has nothing to do with the coelom, but is one of the 

 intestinal pouches characteristic of Auricularia antarclica." It is true that I have not observed 

 the developmental stages of the posterior coelom { — on reexamining the material still at my 

 disposal I do not fiTid any such stages represeided and I feel conlident. therefore, in saying 

 that I have not overlooked these stages, but they were not present in my material — ). It is 

 possible that the vesicle which I represented as the posterior coelom really is the intestinal 

 pouch ( — which I have, otherwise, not at all overlooked, stating, on p. 80, that the rectum 

 "schwillt niehr oder weniger plotzlich an und kann bisweilen den unteren 'reil des .Magens 

 ganz ijberdecken" -). But, anyhow, I have at least not iiusundcrstood the anterior coelom 

 and the hydrocoel. It nuisl certainly Ijc acknowledged that the representation ol the internal 

 structures of Auric, antarclica, given by nie, means a very considerable progress beyond that 

 given by MacBride in his first description of this larva (National .\ntarctic Expedition. 

 Natural History. Vol. VI. Hchinoderma. 1912). and I nnght perhaps suggest that the author 

 of that description was not (piitc riglit in giving as his oidy conunent on my representation 

 of that larva that 1 ha<l "iiuite misunderstood" its coelomic structures. 



