32 



MEDUSJE. I. 



funnel-shaped, with a wide opening into the corners of the stomach; the distal one-third of the radial 

 canal is a narrow tube, communicating with the narrow circular vessel. The umbrellular part of the 

 funnel-shaped canal is narrow, and from this part issue a large number of lateral folds or branches, 

 perpendicular to the main canal. The umbrellular walls of these lateral folds are attached to the sub- 

 umbrella, whence the folds hang as perpendicular lamellse, the \entral edges being free. Below the narrow, 

 lamelliferous part of the radial canal is the wide, funnel-shaped part, mentioned above, reaching out- 

 wards nearly to the outermost (distal) lateral folds, gradually narrowing outwards and terminating 

 in a point. The narrow dorsal part is separated from the wide ventral part by a longitudinal fold on 



each side (Plate III, figs. 2 and 3). These two folds continue in a centri- 

 petal direction in the dorsal wall of the stomach nearly to the centre 

 along both sides of each of the ciliated grooves (Plate III, fig. i). Towards 

 the distal end of the funnel-shaped part the folds are gradually tapering; 

 in the distal part of the folding system there is, accordingly, no complete 

 separation between the ventral and the dorsal part of the canal. Thus a 

 differentiation of the gastro-vascular system, similar to that in Laodicea 

 undulata^ is established in this species. Probably the food is received and 

 dissolved in the wider, ventral part (I have found half-digested copepods 

 therein); the dorsal part only communicates with the ventral part for a 

 short distance near the distal end of the funnel-shaped part. Proximally 

 the dorsal part opens into the dorsal wall of the stomach through a 

 narrow opening, distally it passes into the narrow, tube-shaped part of 

 the radial canal, free of gonads, through which the dissolved nutritive 

 substances, which have been carried from the funnel-shaped part into 

 the dorsal part, are transported further into the circular vessel. 



Seen from the aboral side the systems of transversal folds form 

 together four elliptical figures, commencing at a short distance from the 

 corners of the stomach. In the present specimen the length of the ellipti- 



Flg. 5. Ptychogena lactea A. Agassiz. o i 



A radial canal with its branches cal figures is about 2\ mm, tlie largest breadth about 19 nun, the longest 

 and gonads, seen from the apical 



side — From a specimen from (middle) of the lateral branches being about q mm long, perpendicularly 

 Ritenbenk, Greenland. ' S ^ &. F r 3 



to the main canal. Within this part of the radial canals there are alto- 

 gether 20 — 25 folds on each side of the main canal. Besides these closely set folds there are some 

 short, isolated folds in the lateral walls of the grooves in the dorsal wall of the stomach (see textfig. 

 5, which has been drawn from another specimen). Each of the lateral branches of the radial canals 

 has the shape of a flat, perpendicularly placed pouch, the dorsal edge of which is attached to the 

 subumbrella along a narrow line, and which opens into the main canal by a perpendicular fissure in 

 the narrow, dorsal part of the canal (Plate III, fig. 4). In the walls of these pouches the gonads are 

 developed. The gonads (Plate III, fig. 51 surround the pouch completely except in the line, by which 

 the latter is attached to the subumbrella. Thus the gonads on the two sides of the pouch communi- 

 cate around the free (ventral and distal) edges of tlie pouch. Moreover the gonads of two successive 

 pouches communicate proximally in the perpendicular edge between the openings of the two pouches 



