241 



vided with a simple circumoral ciliated band. This fact is hardly intelli- 

 gible except on the assumption that it represents the original larval type 

 and an ancestral stage in the evolution of the Echinoderm stem. If there 

 is any connection between Coelenterates and Echinoderms, the vestiges 

 of it must be sought for in the structure of the Dipleurula, not in the 

 Crinoids. But I fail to see how this could be found. Possibly the Cteno- 

 phora might have given rise to the Dipleurula — but then these latter are, 

 in my opinion, no Coelenterates. 



It is an established fact that some animal forms have a different mode 

 of development under different biological conditions. As typical instances 

 may be named the shrimp Palsemonetes varians, which has much larger eggs 

 in Southern Europe than in Northern Europe, a corresponding rather con- 

 siderable difference obtaining in the larval development, and Musca corvina 

 which is recorded by Portchinslci to be oviparous in Northern Russia, 

 while in Southern Russia it is viviparous in summertime, oviparous in 

 spring^). Such a remarkable diversity of development, for which Giard has 

 created the name Poiciiogony, was maintained by this author^) to occur 

 also among Echinoderms, Ophiothrix fragilis being especially named as an 

 instance of poiciiogony. This species is stated to develop "suivant les condi- 

 tions ethologiques . . . tantot par des Pluteus normaux (comma dans la Me- 

 diterranee), tantot par des Pluteus imparfaits tels que ceux etudies par Apo- 

 stolides (a Roscoff), tantot meme par des embryons tr^s condenses, inca- 

 pables de nager et qui donnent une Ophiure presque sans metamorphoses 

 (a Vimereux etc.)." (Op. cit. p. 240). This would appear to apply also to 

 a number of other Ophiurids of the North Atlantic, since he states in a 

 previous paper^), likewise reproduced in the "Oeuvres diverses" I. p. 509, 

 that "presque toutes les Ophiures que j'ai observees dans la Manche sont 

 .... vivipares. Je citerai entre autres: V Ophiothrix fragilis et I'Ophiocoma 

 negleda que j'ai plus particulierement etudiees au point de vue de la re- 

 production". ... "A un certain moment del'annee, on trouve des embryons 

 dans toutes les Ophiures que Ton ouvre indistinctement (excepte celles 

 qui sont infestees par les Orthonectida)." 



As I have shown in my paper "On Hermaphroditism in viviparous 

 Ophiurids" (Acta Zool. I. 1920. p. 7—8) this statement of these Ophiu- 

 rids being at times of the year viviparous, while at other times they have 



') J. E. V. Boas. Kleinere carcinologische Mittheilungen. Zool. Jahrb. Abt. f. Syst. 1890. 



2) A. Giard. La Poecilogonie. Congres Internal, de Zool. Bern. 1904. Bull. Scientif. 

 D6p. du Nord de France. 39. 1905. — Reprinted in Oeuvres diverses. I. Biologie G6n6rale. 

 1911. p. 420. 



3) A. Giard. Particularit6s de Reproduction de certains fichinodermes en Rapport avec 

 r^thologie de ces animaux. Bull. Scientif. D6p. du Nord de France. IX. 1878. p. 296. 



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