CTENOPHORA. 33 



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

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

 gastrovascular system 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 Dogielin 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 represent a separate genus 

 within this group, so that the name Dogielia may perhaps be 

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

 .sheaths seems somewhat unusual — ); but the order "Actenae" 

 established for it by Pedaschenko, in any case must be dropped. 

 To Tjalfiella it has evidently no near relation. 



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

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

 tena Salenskii^) is very problematic. In the presence of an apical .^i 



Fig, 8. Hydroctena Salenskii (after 



sense-organ it certainly recalls in some degree the Ctenophores; but Dawydoff). gn. tentacle sheath; 



the fact that there are two otoliths is a prominent difference from °'"^^- 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 possess a strong muscular core as do the tentacles of 

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

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

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

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

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

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

 the genus Solmundclla 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 of Solmundella 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 Dawydoff between Hydroctena and Ctenoplana 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. 18. 1904. p. 569) K. C.Schneider maintains Hydroctena to be 

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

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



M C. Dawydoff. Hydroctena Salenskii, (fitude morphologique sur uu nouveau Coelentere pelagique. Mem. Ac. Imp. 

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



2) R. Woltereck: Bemerkungen zur Rntwicklung der Narconiedusen und Siphonophoren. Verh. d. deutsch. Zool. 

 Gesellsch. 1905. p. 115. 



The Tngolf-Expedilion. V. 2. ^ 



