Introductory notes. 



From the cruise of 1910 the "Michael Sars" brought 

 home an enormous amount of material of Medusae and 

 Siphonophores, which have been handed to me for 

 examination. In this first part of my report I give the 

 results as regards the Scyphomedusae. 



By the systematic use of the same gear in a large 

 series of hauls at different stations, immense numbers of 

 specimens were gathered, which not only afford a good 

 basis for an analysis of systematic details, but also throw 

 light on biological questions, hitherto discussed mostly 

 from a theoretical point of view. Thus the material 

 demonstrates that the intensity of pigmentation corre- 

 sponds with the bathymetrical distribution of some of the 

 species, also enabling us to determine both the bathy- 

 metrical range and the maximum development of little 

 known deep-sea Medusae. 



The number of species collected is not large, very 

 few coastal forms having been taken during the cruise. 

 The material includes the following 10 species, two of 

 which seem to be new to science, both typical deep-sea 

 Medusae: 



Periphylla hyacinthina Steenstrup. 



„ regina Haeckel. 



Nausithoe atlantica, n. sp. 



„ glob if era, n. sp. 



Atolla Wyvillei Haeckel. 



„ Balrdi Fewkes. 

 Pelagia perla Slabber. 



Chrysaora mediterranea Peron and Lesueur. 

 Poralla rufescens Vanhoffen (?). 

 Aurelia solida Browne. 



The locality is new for Atolla Wyvillei, which had 

 not previously been found in the Atlantic area, north- 

 wards of the subantarctic region, and the northern limit 

 of Periphylla regina is extended far to the north of 

 previous records. One species (Periphylla regina) is new 

 for the Mediterranean, and the occurrence of the genus 

 Poralia in the Atlantic is of great zoogeographical interest. 



Investigations of the plankton and its biology have 

 taught us to distinguish between holoplanktonic 

 organisms (Holoplankton), confined to oceanic 

 waters during their whole lifetime, and mero plank- 

 tonic organisms (Meroplankton) confined to 

 coastal waters. This terminology was first employed by 

 Haeckel, and is now generally adopted. Fowler has 

 introduced a new word epiplankton instead of mero- 

 plankton, but this word is both superfluous and misleading. 

 Unfortunately some of the younger specialists in single 

 plankton groups use Fowler's term, and Ritter-Zahony 

 for example has thereby brought confusion into the ter- 

 minology of the Plankton-Expedition 1 ) and the Fauna 

 arctica 2 ); he gives us the rather surprising news that 

 many chaetognaths are "epiplanktonic". This word 

 is meant to designate organisms fixed on 

 planktonic plants or animals, and in this sense 

 it is found in every elementary treatise on plankton 3 ). 



It is especially among the Hydromedusae that we 

 find many well-known examples of neritic organisms, 

 i. e. meroplanktonic organisms which pass 

 through a fixed bottom-stage, while a great 

 many Scyphomedusae are also neritic. 



Of the ten species collected by the "Michael Sars" 

 the majority are holoplanktonic, and only Pelagia perla 

 is an inhabitant of the photic zone. Seven of them, viz. 

 Periphylla hyacinthina, P. regina, Nausithoe atlantica, 

 N. globifera, Atolla Wyvillei, A. Bairdi, and Poralia sp., are 

 true deep-sea Medusae, although one of these (Periphylla 

 hyacinthina) also occurs sometimes in depth less than 

 300 metres. 



All these forms are of a purple brownish-black colour, 

 apparently on the whole the typical colour of most deep- 

 sea Medusae. The pigmentation is mostly confined to 

 the gastro-genital system, and varies in intensity according 

 to the bathymetrical habitat of the individual. Pelagia 

 in its varying and rather vivid colouring is like the neritic 

 species Chrysaora mediterranea and Aurelia solida, the 

 surface Medusae showing a far greater limpidity than 

 most deep-sea species. 



') Die Chatognathen, Wiss. Ergebn. d. Planktonexpedition. Kiel 1911. 

 ') Die Chatognathen, Fauna arctica, Bd. V. Jena 1910. 

 3 ) See for instance Steuer's Planktonkunde. 



