CTENOPHORA. ,, 



the swimming plates) liaving- been lost through the handling of the animal in the net. The more 

 remarkable circimistance here is not the disappearance of the jelly and the skin, but the fact that the 

 gastrovascular s\^stem has remained in connection as a sort of "skeleton"; though remarkable enough 

 it is, however, much less improbable than the existence of an animal without skin. 



The Dogiflin thus explained is no longer one of the most 

 aberrant Ctenophores made known; it very probably belongs to the 

 Cydippids. Possibly it will prove to reijresent a separate genus 

 within this group, so that the name DogieUa ma>- perhaps be 

 retained | — the relation of the interradial vessels to the tentacular 

 sheaths seems somewhat unusual — ); but the order "Actense" 

 established for it b\' Pedaschenko, in an\- case must be dropped. 

 To Tjalficlla it has evidently no near relation. -"•"»' 



While there is no doubt that the DogieUa is really a Ctenophore, 

 or at least part of a Ctenophore, the Ctenophoran nature of the Hydroc- 

 tcna Solciiskii'^) is \ery problematic. In the presence of an apical -' 



. , ^ , ^iS- ^- Hydrocti-na Salenskii (after 



sense-organ it certainlv recalls in some degree the Ctenophores; but Da wy doff), gn. tentacle sheath; 



the fact that there are two otoliths is a prominent difference from "i"br. manubrium; org. ab. apical or- 

 gan; tcl. tentacle; vl. velum. 

 the Ctenophores, which have always only one otolith. Another 



fact recalling the Ctenophores is the existence of only two, aboral, retractile tentacles, lodged 

 within well developed tentacle sheaths. They jDossess a strong muscular core as do the tentacles of 

 the Ctenophores, in decided contrast to the Hydromedusse. But here the resemblances stop; and the 

 differences are certainly much more important. There is a well developed velum and manubrium 

 but no costas; no colloblasts are found, but cnidoblasts. The whole histological structure is quite 

 different from that of Ctenophores. I fully agree with A. G. Mayer (Medusae of the World. II. 1910. 

 p. 459) that the resemblances between Hyc/rocfena and Ctenophores are "merely parallelisms, none of 

 which indicate a genetic relationship with Ctenophorse". Hydroctcna is a Narcomedusa, resembling 

 the genus Solinundella in all respects, excepting its apical sense-organ, peculiar structure of the ten- 

 tacles and the absence of marginal sense-organs, the resemblance being rendered closer b\- the 

 recent discovery by Woltereck^) that the larva oi Soliimudclla has a ciliated, apical pole-plate. Thus 

 the only feature remaining exceptional for a Narcomedusa is the muscular core of the tentacles. — 

 The parallelism sought by Da wy doff between Hydyoctena and Cfcnoplann in the structure of the 

 excretory vessels is accordingly, at most, an analogy, viz. in case these vessels really do not open to 

 the exterior in Ctenoplana, as is maintained by both Korotneff and Willey, but which can, by no 

 means, be regarded as an established fact. — In his note "Systematische Stellung von Hydroctena 

 salenskii" (Zool. Anzeiger. XXVII. Nr. :8. 1904. p. 569) K. C. vSchneider maintains Hydroctena to be 

 a true Ctenophore; the undeniabe resemblances to the HydroniedusEe are regarded as "Konvergenz- 

 ercheinungen". Schneider "homologisiert ohne weiteres die sog. Subumbrella samt Velum mit dem 



M C. Dawydoff. Hydroctena Salenskii, (Etude niorphologique sur un nouveau Coelentere pelagique. Mem. Ac. Imp. 

 d. Sci. St. Petersbourg. 8. Ser. XIV. Nr. 9 1904. 



2) R. Woltereck: Bemerkungen zur lintwicklung der Narconiedusen un<l Siphonophoren. Verli. d. deutsch. Zool. 

 Gesellsch, 1905. p. 115. 



The Ingolf-Expedition. V. 2. *^ 



