MEDUSA. I. 57 



to me the most probable that the breeding of the medusa takes place at the end of the autumn or 

 in the winter, that the unknown polyp-generation lives during the later winter months and deliberates 

 the medusae in the first spring-months; the medusae then appear in the fjords in May or later and 

 grow to maturity in the course of the summer and autumn. 



The finds at Port Erin and Valencia Harbour were made on May 26th and ajth and on June 

 and and July igth (altogether 4 finds, according to Browne 1900 and Delap 1905). There are two 

 possible explanations of these finds: The few specimens, mentioned by the said authors, may have 

 been carried southwards after their deliberation from the polyps; but as the dates of the finds are 

 mostly antecedent of the season, at which the species is most numerous in the northernmore regions, 

 there is also the possibility that they have been deliberated in the neighbourhood of the finding- 

 places from hydroids originating from medusae, which were carried down there in the preceding 

 winter or autumn, that the hydroid, accordingly, is able to live here in the winter, as also the medusae 

 may pass the spring but die away towards the hot summer time. Both explanations give the result, 

 that the whole cyclus of development cannot be traversed on the spot, but new specimens must be 

 imported every year. From the data now in hand it is impossible to state with certainty, which of 

 the two possibilities is the correct one. It seems to me, however, that the first explanation is the more 

 probable, as it appears that the species is able to live in the Danish waters in the warmest months of 

 the year. 



As far as the Danish waters are concerned, the facts lie more clearly. All finds from the Katte- 

 gat have been made between medio June and medio August. According to Mobius it occurs at Kiel 

 in October November. In the eastern part of the Skagerrak it has been found in November (Inter- 

 national Plankton Catalogues). Nothing indicates that the polyp generation should live in the Danish 

 waters. The medusae found here have undoubtedly been imported by the current. They are able to 

 keep themselves alive in our seas during the hot summer months, but it is very improbable that they 

 ever breed here. More detailed records of the occurrence of Melicertum octocostatum in the Danish 

 waters will appear in a future paper. 



Melicertum campanula L. Agassiz. 



As mentioned above this species is possibly identical with Melicertum octocostatum Sars. It occurs at the eastern coasts 

 of North America, being common from Eastport to Cape Cod. It has been mentioned from that area by the following authors : 

 L. Agassiz (1862, p. 349), A. Agassiz (1865, p. 130134), Verrill (1871, p. 6), Fewkes (1888 a, p. 233), Mayer (1910, p. 207;, 

 Bigelow (19143, p. 125; 1914 b, p. n; 1915, p. 316, 319, 320). South of Cape Cod it has only been taken once, viz. at Woods 

 Hole (Nutting 1901, p. 382). 



According to these authors the species appears at the coasts of New England in May and disappears in July or Au- 

 gust. Young individuals are found in the spring. 



Bigelow characterises it as boreal-neritic; it has never been found more than 10 miles from the shore. 



Genus Dipleurosoma Boeck. 

 Dipleurosoma typicum Boeck. 



Mayer 1910, Medusae of the World, p. 224. 



Bell usually flatter than a hemisphere and about 15 mm in diameter. Stomach flat, with an irregular outline; there 

 are four lips. The number of radial canals arising from the periphery of the stomach ranges from 5 to 18; they branch in an 



The Ingolf.Expedition. V. 8. 8 



