240 



mains in open connection wilh Ihe body cavity Ihroughoul life, which is 

 taken as a proof that the C.rinoids are the most primitive of all Kchi- 

 no(iernis'). 11 would aj)pear llial the auliior has onlirely overlooked the fact, 

 established beyond any doiibl, es])eeially lhroui»h Seel if»er's researches '^), 

 ( — his results being fully confirmed by my own researches ) that the 

 coniu'clioii between the water-vascular system ami llii- body cavity in 

 Anledoi} is only a secondary character, arising at a rather late stage of de- 

 velopment (in the Pentacrinoid-stage). Accordingly this is no primitive 

 feature and cannot alTord any proof of relationship with the Coelenlerales. 

 The (^rinoid-larva is regarded as the most primitive of Echinoderm- 

 larvae, "nahert sich viel mehr dviu (loelenteraten-Larven-Typus, ist jeden- 

 falls (hirchaus anderer (iestalt als die (Ivv anderen Echinodermen, uiid da 

 diese Larve derurspriinglichslen Kchinodermen-Abteilung angeluHl, hat 

 sie bei der l>eurteilung der N'erwandtschaflsbe/.iehungen ein grosseres In- 

 teresse als che andere, aus deren liau sicii nicht auf (he Abstamnuing der 

 lu'hinodermen Schliisse ziehen lassen". The typical pelagic, bilaleial larval 

 foiiu ■kauM icli (lioas) natiirlicii nur als eine ganz sekundiire beurteilen. 

 Diesclbe ist bekanntlich . . . noch nichl bei den Crinoiden ausgebildet, 

 deren Larve mit fiinf Wimperringen umzingelt ist, von denen vier alien 

 radiiiren Anforderungen geniigen." (Op. cit. p. 23). — I may refer to the 

 remarks given above in criticism of the view, also expressed by Grave, 

 thai the larva with the ciliated rings is the primitive larval form of Echi- 

 noderms. Especially Ihe structure of the T/i/edon-larva is anything but 

 primitive, but only inlelligible as a special adaptation of the simpler ty|)e 

 of the pelagic hiiva- to the conditions of the yolky eggs, as it is found 

 likewise in other barrel-sliaped larva* devel()])ing from eggs with a rich 

 content of yolk. On the contiary, as staled above (p. 232). there is every 

 reason to suppose that there was also a typical bilateral larval form at 

 least in some of Hie numerous fossil Pelmatozoa, should i I even be proved 

 that none of the few surviving types have such a larva. The lather bold 

 assertion that no conclusions as regards the ancestry of h^chinodeinis can 

 be drawn from the struclure of the typical larva* does not do away with 

 the fact that all these larva* pass through the ■■l)ipleurula"-stage, that is 

 to say, begin as a simple, bilateral, wormshaped organism with a segmented 

 body cavity consisting of at least two, probably three segments, and pro- 



') From the Crinoids Ihe Asteroids are derived and from the latter again the Ophi- 

 urids and Echinoids, the Hololluirians liaving arisen from the Echinoids. Witiiout entering 

 on a discussion of this view of the genetic interrelations of the classes of recent Echi- 

 noderms I would merely express my astonishment at a fancy bold enough to conceive 

 the derivation of Asteroids from the Crinoids. 



-) O. Seeliger. Studien /ur l^ntwicklungsgeschichte der Oinoidcn. Zool. Jahrb. .\l)t. f. 

 Anat. u. Onlog. VI. 189.{. 



