74 



MEDUSA. I. 



The map (Chart IX) demonstrates that the North-European localities, in which this species 

 has been found, fall into two separated groups: i) south of Iceland, 2) west of the British Isles. Though 

 these areas are very near each other, there seems, however, to exist an obvious difference between the 

 individuals from the two areas, in any case in one regard, in so far as the specimens from Iceland 

 have a greater number of radial canals than the British specimens of corresponding sizes. In Table 

 VII, which serves to elucidate this fact, the .specimens collected by the "Michael Sars" in 1910 are 

 included among the specimens from the British area. 



Also with regard to the relation between the diameters of the stomach and the umbrella there 

 seems to be a difference between the British and the Icelandic specimens, the stomach being compa- 

 rativelv larger in the former than in the latter. 



Table VII. Numbers of radial canals of specimens of different sizes 



of Halopsis occLlata. 



I have measured the stomachs in 21 Icelandic and 10 British specimens, and I give the figu- 

 res obtained in Table VIII, at the same time as I expressly remark that too much importance must 

 not at present be ai)plied to the results, the material investigated being rather small. The figures 

 look, however, interesting as far as they indicate the existence of two different local races in areas 

 very near each other; if future investigations should confirm this result, it would be of great interest 

 to the studies of the variation of medusas. 



It will be observed from the table that, as far as the smaller and middle-sized individuals are 

 concerned, the figures representing the proportion between the size of the stomach and that of the 

 umbrella exhibit a somewhat considerable difference between the specimens from the two areas. The 

 figures from Iceland show, moreover, that the stomach grows in size nearly proportionately to the 

 umbrella until the latter has reached a diameter of towards 40 mm; at this size the sexual products 



