240 



mains in open connection with the body cavity throughout life, which is 

 taken as a proof that the Crinoids are the most primitive of all Echi- 

 noderms 1 ). It would appear that the author has entirely overlooked the fact, 

 established beyond any doubt, especially through Seeliger's researches 2 ), 

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

 connection between the water-vascular system and the body cavity in 

 Antedon 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 afford any proof of relationship with the Coelenterates. 

 The Crinoid-larva is regarded as the most primitive of Echinoderm- 

 larvse, "nahert sich viel mehr dem Coelenteraten-Larven-Typus, ist jeden- 

 falls durchaus anderer Gestalt als die der anderen Echinodermen, und da 

 diese Larve der ursprt'mglichsten Echinodermen-Abteilung angehorl, hat 

 sie bei der Beurteilung der Verwandtschaftsbeziehungen ein grosseres In- 

 teresse als die andere, aus deren Ban sich nicht auf die Abstammung der 

 Echinodermen Schliisse ziehen lassen". The typical pelagic, bilateral larval 

 form "kann ich (Boas) naturlich nur als eine gan/ sekundare beurteilen. 

 Dieselbe ist bekanntlich . . . noch nicht bei den Crinoiden ausgebilclet, 

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

 radiaren Anforderungen genugen." (Op. cit. p. 23). - - I may refer to the 

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

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

 uoderms. Especially the structure of the /l/i/edo/7-larva is anything but 

 primitive, but only intelligible as a special adaptation of the simpler type 

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

 likewise in other barrel-shaped larvae developing from eggs with a rich 

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

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

 least in some of the numerous fossil Pelmatozoa, should it even be proved 

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

 assertion that no conclusions as regards the ancestry of Echinoderms can 

 be drawn from the structure of the typical larvae does not do away with 

 the fact that all these larvae pass through the Dipleurula"-stage, that is 

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

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



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

 urids and Echinoids, the Holothurians having arisen from the Echinoids. Without 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. 



2 ) O. Seeliger. Studien zur Entwicklungsgeschichte der Crinoiden. Zool. Jahrb. Abt. f. 

 Anat. u. Ontog. VI. 1893. 



