8 4 



CTENOPHORA. 



Ctenophoren d. Plankton-Exped. p. 27) points out more precisely as the difference between the arctic 

 B, cucumis and the Mediterranean-Atlantic B. ovata that "bei Beroe cucumis enden die auf die Magen- 

 wand iibertretenden Prolifikationen der Meridionalgefassen blind, ohne ein anastomosirendes Netzwerk 

 von Gefassmaschen zu bilden, welches mit dem Magengefass kommuniziert; bei B. ovata anastomosiert 

 ein Teil der Gefassprolifikationen, indem sie niclit nur unter sich, sondern auch mit dem Magengefasse 

 Verbindungen eingehen". 



This is accepted by Vanhoffen in his "Ctenophoren" in "Nordisches Plankton" and especially 

 by Moser (Japanische Ctenophoren, p. 19), who gives the difference between the two species more 

 precisely thus: "Bei Beroe cucumis sind, im Gegensatz zu den Meridionalgefassen, die Magengefasse 

 unverzweigt; die auf die Magenwand iibertretenden Prolifikationen der Meridionalgefasse enden blind. 

 Bei Beroe ovata sind auch die Magengefasse verzweigt; ihre Aste bilden mit jenen der Meridional- 

 gefasse ein anastomosierendes Netzwerk auf der Magenwand". It is further maintained (p. 21) that 

 Beroe ovata "eine ausschliesslich mediterrane Form ist, wahren aus den Funden von Ambon und von 

 der japanischen Kiiste hervorgeht, dass Beroe cucumis nicht eine exklusiv nordische und atlautische 

 Form ist, sondern auch in den warmen Meeren vorkommt und ein Kosmopolit im weitesten Sinne 

 des Wortes ist". 



After this definition it seems easy enough to distinguish the two species, and the alleged 

 occurrence exclusively in the Mediterranean J ) of B. ovata, while B. cucumis is not known to occur there, 

 would alone seem to make it impossible to confuse the two species. But nature does not agree with 

 this; the sharp distinction between the two forms does not really exist. From a careful study of a large 

 material of Beroe from the Danish and Norwegian Seas, from Greenland, from the Atlantic and the 

 Mediterranean I have found all transitional stages to exist in regard to the development of prolifer- 

 ations from the pharyngeal vessels, from the highly branched condition characterizing the "species" 

 ovata to the unbranched condition characterizing the "species" cucumis. My attention was first called 

 to this fact by the examination of a number of specimens from the Godthaab Fjord, Greenland, 

 brought home by Mr. Ad. S. Jensen from the "Tjalfe"-Expedition. Some of these specimens had the 

 pharyngeal vessels quite unbranched, while others had them more or less richly provided with alter- 

 nating proliferations. That the differences in this respect were not due to growth-changes, was evident 

 from the fact that the proliferations were developed in a specimen of io mm length, while in other 

 specimens of 15""" length no proliferations at all were developed. All these specimens were in all 

 other regards so decidedly alike that it would be quite unreasonable to separate them into two species. 

 The same differences were found in specimens from another Greenland locality (Holstensborg). Among 

 a considerable number of specimens from the Skagerak, which I collected in June 1911 on the "Thor", 



') R. T. Giinther (Report on the Coelenterata from the intermediate waters of the N. Atlantic obtained by 

 Mr. George Murray during the Cruise of the "Oceana" in 1898. Ann. Nat. Hist. 6. Ser. XI. 1903. p. 429) certainly mentions Beroe 

 ovata; but there is no guarantee at all that this was really another species than 11. cucumis. That the B. ovata mentioned by Hart- 

 laub (Beitrage zur Meeresfauna von Helgoland. IV. Die Coelenteraten Helgolands. Wiss. Meeresuntersuchungen. N. F. II. 

 1894. p. 204) is really B. cucumis, has been shown by Moser (Japanische Ctenophoren, p. 20). M. & C. Delap (Notes on the 

 Plankton of Valencia Harbour. 1899-1901. Ann. Rep. Fish. Ireland. 19023. Pt. II. App. I. 1905. p. 5) record Beroe ovata Esch. 

 as the only Beroid occurring at this locality. That it is the same as B. cucumis can scarcely be doubted. Also Evans & Ash- 

 worth (Some Medusae and Ctenophores from the Firth of Forth. Proc. R. Phys. Soc. XVII. 1909. p. 311) state that "in this 

 area the specific names ovata and cucumis have doubtless been applied to the same form". Romer (Op. cit p. 85), gives several 

 other instances, where B. ovata has been recorded from the North European Seas. The Beroe ovata mentioned by Fewkes 

 and Hargitt (se below, p. 86) may perhaps be something different (Beroe Clarkii). 



