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 Pahrmoneles 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 Portchinski to be oviparous in Northern Russia, 

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

 spring 1 ). Such a remarkable diversity of development, for which Giard has 

 created the name Poicilogony, was maintained by this author 2 ) to occur 

 also among Echinoderms, Ophioihrix fragilis being especially named as an 

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

 tions ethologiques . . . tanlot par des Pluleus normaux (comme dans la Me- 

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

 stolides (a Roscoff), tantot meme par des embryons tres condenses, inca- 

 pables de nager et qui donnent line 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 3 ), 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: rOphiothri.r frayilis et VOphiocomn 

 ne(/lccl(i que j'ai plus particulierement etudiees au point de vue de la re- 

 production". ... "A un certain moment de 1'annee, on trouve des embryons 

 dans loutes les Ophiures que Ton onvre indistinctement (excepte celles 

 qui soul infestees par les Orthoneclida)." 



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

 Ophiurids" (Ada Zool. I. 11)20. p. 7 <S) this statement of these Ophiu- 

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



') .1. I"., v. Boas. Kleinere carcinologtsche MittheUungen. Xool. .Jahrb. Al>t. f. Sy.t. I.S'.KI. 

 i \. Giard. La Poecilogonle. C.ongres Internal, de Xool. Bern. 1904. Bull. Scientif. 

 l)ep. (In Nord dc I-'rani'i 1 . .'{'.I. I'.HI.'I. - Reprinted in Oi-uvn-s diverses. I. Biologic (lencrale. 

 11111. p. -120. 



3 ) A. Giard. 1'articularitcs de Reproduction de certains chinodermes en Rapport avec 

 I'l'tholofjic dc CCS animaux. Bull. Scienlif. l)cp. du Nord dc I-'rance. IX. 1S7S. p. 1206. 



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