236 



a soinewlial more detailed study as regards the development and gradual 

 transt'ormalion of the inner structures. The results accjuired from Ihe study 

 of these ohjeels, I hough liiey cannot claim lo be of nu)re general value, 

 are in themselves of very great interest and throw imjiortanl light on 

 several |)rol)lems connecled with liie developmenlal iiistory of Echino- 

 derms. 



The mosl interesting of the facts discovered by the study of the said 

 forms with abbreviated development would ap|)ear lo be that of the am- 

 nion develo])ing from the pharynx in Pcioiielld Lesuciiri, while other- 

 wise it develops as an invagination from the ectoderm on the left side of 

 the larva, above the hydrocoel. (In llcliociddiis eriithronrainma il could not 

 be decided whether il likewise develops on the left side, there being a])par- 

 enlly no uieans of identifying the right and the lefl sides in this perfectly 

 cylindrical larva). This may perhaps give some indication as lo the way 

 in which Ihe anuiion of hxhinoid-larvse originated. MacHride has come 



10 the conclusion thai the amniotic cavity of Ihe pAhiuo|)luleus may be 

 interpreted as a portion ol the stoiuoda'uiii which is formed separately 

 from liie rest of it'), because in the metamorphosing larva of Opiiiuthri.r 

 jnK/His he has found the primary lubefeel protruding into the stomodseuni. 

 The fact that the amnion of Peronclht Lcsiicuri does originate as an out- 

 growth from the pharynx would seem to lend an emphatic support to 

 MacBride's theory. Still I would not take it as having been delinitely 

 proved as yet by these facts. Peronella Lcsueuri is a very highly sj^ecial- 

 ized type; may w-e then really rely upon this remarkable development of 

 the amnion in the much reduced larva as meaning a reversion to Ihe pri- 

 mitive mode of development? It is ])erha|)s not quite safe to draw this 

 conclusion as yet. If other similar cases were found, the conclusion would 

 be very considerably strengthened; but this isolated, evidently very spe- 

 cialized case does not seem l(* me lo afi'ord suflicient proof. Neither does 

 the OphiolhrixAarva appear to me to be a sufficient proof of the liieory. 



11 is the only Ophiuran with a typical pelagic larva liie metamorphosis 

 of which has been adequately studied as yet. But the little we know about 

 the metamorphosis of other Ophioplutei does not point towards the slomo- 

 dteum as iiaving generally the funclion of an amnion in Ophiurid-larva'. 

 In Ophiopluleus binmculalus, so carefully studied by .loh. .Miiller"'^) and 

 Metschnikof f ^) — though not by means of sections, of couisc il ap- 

 pears that the su boral cavity has got liie function o f a n amniotic 



') .MacBridi'. Textbook ol Knil)ryolof<y. 1. Iiiverlcbrala. 1914. p. .")22. 

 ■-) Joh. Miillcr. ('bcr die Ophiurenlarveii d. Adrialischen Mecres (V. Abliaiidl. 1852), 

 Taf. II— III. 



') E. Metschiiitiofl. Sludieii iiber die Hnlw. d. Echiiiod. u. .Xeinerlinen. Taf. VI^VIl. 



