66 



MEDUSA. I. 



The diameter of the largest specimen at my disposal is about 56 mm. The manubrium consists of a 

 flattened stomach (Plate IV, fig. i), circular or star-shaped in outline, and a short mouth-tube. The dia- 

 meter of the stomach is about one-fifth the diameter of the disk. The length of the mouth-tube of a 

 well-grown specimen is about 4 mm, its diameter at the narrowest part about one-half the diameter of 

 the stomach. The lower (distal) part of the mouth-tube is somewhat expanded, divided into 4 folded lips 

 separated by 4 slight incurvations, not by deep incisions. The stomach is fastened to the subumbrella along 

 the edges of the proximal parts of the radial canals, thus a number of triangular pouches existing between 

 the subumbrella and the dorsal wall of the stomach. The number of radial canals varies (in the pre- 

 sent material) from 12 to 17; the canals are arranged in four clusters (Plate IV, fig. i). From the cen- 

 tral point four canals issue, each of which is very soon divided into 3 5 branches; as a rule the 

 branching is completed within the outline of the stomach, so that apparently the radial canals arise 

 separately from the periphery of the latter. The fully developed canals reach the circular vessel, 



Fig. 6. Fig. 7. Fig. 8. 



Fig. 6. Halopsis ocellata A. Agassiz. Transversal section through a radial canal with male gonads. X 85. - - Fig. 7. Halopsis 

 ocellata A. Agassiz. Transversal section through a radial canal with female gonads. Three of the eggs are ready for liberation. 

 X 120. Fig. 8. Halopsis ocellata A. Agassiz. Transverse section through the distal part of a radial canal, free of gonads. 06s. 



the high development of the entoderm and the narrow lumen, x 240. 



but sometimes we may find young canals terminating blindly somewhere on the subumbrella (textfigs. 

 9 c,f, h, k). The points of connection between the radial canals and the circular vessel are, as a rule, 

 not equidistant. The stomach sends out a short conical prolongation along each of the radial 

 canals (Plate IV, figs, i and 5). The lines of attachment of the radial canals to the subumbrella 

 are very narrow (Plate IV, figs, i and 5; textfigs. 6, 7, 8). The gonads (Plate IV, figs, i, 3, 4; textfigs. 

 6 and 7) are situated along the radial canals, forming a narrow, somewhat folded band on each side 

 of the canal, leaving both ends free. The gonads commence at a distance of 2 7 mm from the peri- 

 phery of the stomach and terminate i 2 mm from the circular vessel. The dorso-ventral extension of 

 the gonadial bands comprises nearly the whole of the lateral walls of the canals, commencing very 

 close to the subumbrella and ventrally leaving but a very narrow line to separate the gonads of the 

 two sides (textfigs. 6 and 7). In the short distal part of the radial canals, free of gonads, the entoderm 

 is highly developed, so that in this part the lumen of the canal is quite narrow (textfig. 8). 



There is a large number of hollow tentacles (Plate IV, fig. 2), fairly long and very contractile; 



