234 



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

 plutei. It was discovered by Metschnikoff and made the object of a 

 closer study especially by Semon in his paper on "Die Entwickelung der 

 Synapta digitata" 1 ); furthermore Chun described the nervous system of 

 Auricularia nudibranchiata, while it was observed by myself in Auricularia 

 antarctica, all these forms agreeing very closely in regard to the shape 

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

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

 sentation of the nervous system of Auricularia antarctica (PI. I, Figs. 1 2) 

 quite different 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 that 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, Fig. 1), such as it was also found by Chun in Auri- 

 cularia nudibranchiata. I do not want to deny the possibility that this 

 structure may be of a nervous 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 2 ). 



In the Ophiurid-larvse 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-larvse 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. Zeitschr. f. Naturwiss. XXII. 



2 ) I may take the opportunity here to object to a statement by MacBride concerning 

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

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

 that represented in text-fig. 1 in Mortensen's latest paper, but M. has quite misunderstood it. 

 He overlooked the rudiment of the posterior coelom altogether, and has figured a sac entirely 

 detached from the anterior coelom as the posterior enterocoele. This sac, which 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 antarctica." 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 find any such stages represented and I feel confident, 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 mehr oder weniger plotzlich an und kann bisweilen den unteren Teil des Magens 

 ganz iiberdecken" ). But, anyhow, I have at least not misunderstood the anterior coelom 

 and the hydrocoel. It must certainly be acknowledged that the representation of the internal 

 structures of Auric, anlarctica, given by me, means a very considerable progress beyond that 

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

 Natural History. Vol. VI. Echinoderma. 1912), and I might perhaps suggest that the author 

 of that description was not quite right in giving as his only comment on my representation 

 of that larva that I had "quite misunderstood" its coelomic structures. 



