MEDUSA. I. 



The material contains a. number of young individuals, viz. from the "Michael Sars", south of 

 the Myrdalsj0kel, Iceland, '7/ 8 1903; from the "Thor" stat. 45(08), Iceland; from two localities near the 

 Hebrides, "Thor" stat. 8(08) and n (08); and from the Horns Rev light-vessel, west of Jutland, 2 3/ 9 1912. 

 The smallest specimen is 5 mm wide. These young individuals show that the margins of the dorsal 

 grooves in the wall of the stomach begin at an early stage to develop into folds which meet and 

 transform a part of the groove into a closed canal; further that the gonads first appear near the 

 corners of the stomach and, from these points, develop partly in a centripetal direction towards the 

 centre of the stomach, which is, however, never reached, partly in an outward direction towards the 

 circular vessel, which is, likewise, never reached. At an early stage the transversal folds of the gonads 

 begin to form; in a specimen, 7 mm wide, each of the gonads has 23 pairs of transversal folds; in 

 an individual, 9 mm wide, there are 6 pairs of folds on each of the gonads. When the diameter of the 

 bell is about 20 mm, the gonads are somewhat far developed, particularly the female gonads, which 

 already now contain very conspicuous eggs. 



The structure, mentioned above: that the ventral, funnel-shaped part of the radial canal is 

 separated from the dorsal gonadial part by two lateral longitudinal folds, does not seem to have been 

 observed by previous authors. In this part of the gastro-genital system there is established a very 

 interesting differentiation into two parts with different functions. The ventral, funnel-shaped part 

 receives and dissolves the organisms, which serve as food for the medusa; they are however prevented 

 from penetrating into the dorsal part between the gonads on account of the longitudinal folds; the 

 dissolved nutritive matter, on the other hand, may pass between the folds into the dorsal part Prob- 

 ably a part of the food is also digested in the stomach and may, by means of the ciliary motion in 

 the dorsal grooves, be carried into the dorsal part of the radial canal; this part, accordingly, has two 

 functions: to carry the gonads in its lateral walls, and to transport the nutritive substances into the 

 peripheral parts of the canal system. 



From what is said above with regard to the development of the gonads, it will be understood, 

 that the length of the distal part of the radial canals free of gonads in proportion to the radius of 

 the bell is considerably larger in young specimens than it is in full-grown individuals. In specimens, 

 about 10 mm wide, the gonads reach to the middle of the radial canals. In full-grown individuals the 

 length of the gonads is very variable. In a specimen, 28 mm wide, from Iceland ("Thor" stat. 241 (09)) 

 the distance from the distal end of the gonads to the circular vessel is 2 mm; in another specimen, 

 30 mm wide ("Thor" stat. Da. 13 (04)), the length of the gonads is 9.5 mm; they commence 1.5 mm from 

 the centre of the stomach and terminate about 4mm from the circular vessel; in a specimen, 35mm 

 wide ("Thor" stat. 180(04)), the length of the gonads is about 15 mm; they commence very near the 

 centre of the stomach and terminate 2.5 mm from the circular vessel. 



The number of tentacles is considerably larger than is usually stated in the literature. It is 

 possible that the locality plays a part in this respect. All the specimens examined by me have been 

 found in the waters around Scotland, the Faeroe Islands, Iceland, Norway, and Denmark. The smallest 

 individual is from the Horns Rev light-vessel, 2 3/ g 1912; it is 5 mm wide and has about 48 tentacles, 

 placed at some distance from each other; in accordance herewith the basal bulbs are comparatively 

 broad. Specimens from the waters near the Hebrides ("Thor" stat. 8 (08) and 1 1 (08)) have, when 7 mm 



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