211 



vided with a simpU' ciicuinoral ciliated band. This fact is hardly intelli- 

 gible except on llie assumption Uiat it represents the original larval type 

 and an ancestral stage in the evolution of the I'Lchinoderni stem. If there 

 is any connection between Coelenterates and Echinoderms, the vestiges 

 of it must be sought i'oi- in I lie structure of the Dipleurula, not in the 

 Crinoids. But 1 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 ditTerenl mode 

 of development under difTerent biological conditions. As typical instances 

 may be named the shrimp Pula^monetes uarians. which has much larger eggs 

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

 siderable diil'erence obtaining in the larval development, and Musca corvina 

 which is recorded by Port chin ski to be oviparous in Xorthern 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 Poicilogony, was maintained by this author-) to occur 

 also among Echinoderms, Ophiolhiix fragilis being especially named as an 

 instance of poicilogony. This s[)ecies is stated to develop "suivant les condi- 

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

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

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

 pables de nager et qui donnent une Ophiure presque sans metamorphoses 

 (a Vimereux etc.)." (Op. cit. [). 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: VOphioihrix fragilis et VOphiocoma 

 neqlevta que j'ai plus particulierement etudiees au point de vue de la i;e- 

 |)roduction'". . . . ""A un certain moment de I'annee, on trouve des embryons 

 dans toutes les Ophiures que I'on ouvre indistinctement (excepte celles 

 qui sont infestees par les Orthonectida)." 



.\s 1 have shown in my paper "On Hermaphroditism in viviparous 

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

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



') .J. Iv v. Boas. Kk'iiuTt' carcinolof^isclu' Mittlicilungcii. Zool. Jahrb. .\bt. f. Syst. 1800. 



') A. (liard. La Poi'i-ilojjonic. ("ongres IiUeriiat. do Zool. licrn. 1001. Bull. Scicntif. 

 D(^p. dii Nord de l'"raiu'i'. HO. 100."). - Reprinted in Oeuvres diverses. I. Biologic Geiierale. 

 1911. p. 120. 



') \. Giard. I'arlieularites de Beproduition de certains l-xliinoilcrmcs eii Happorl avcc 

 Icthologie de ces aniniaux. Bull. Scicntif. I)cp. du N'ord de France. IX. 1878. p. 206. 



31 



