AURELIA AURITA 43 



with the fringe of labial tentacles, longitudinal groove and 

 brood-pouches filled with developing eggs; mouth, four gastric 

 pouches with gastric ostia, gonadial grooves, gonads and gastric 

 filaments; four perradial canals, of which only two running at 

 right angles to each other should be drawn with all branches, of 

 the other two merely their beginning; one interradial canal with 

 all its branches in the quadrant between the two finished per- 

 radial canals; two adradial canals of the same quadrant; the cir- 

 cular canal; the eight rhopalia or marginal sense organs; the 

 tentacles all around the edge of the disc; the four openings of the 

 subgenital pits over the centres of the gastric pouches. Label all 

 above structures as well as the perradial, interradial and adradial 

 planes. 



2. Cut off with scissors a piece of the margin with a rhopalium. 

 Place it in a Syracuse dish in as little water as possible and turn 

 the piece so that its exumbral surface would be uppermost. 

 Examine under low power (50 diameters) the rhopalium and the 

 surrounding structures. Make a half page drawing showing 

 the hollow tentacles with swollen base, the protective fold, in 

 it the tentaculocyst, the two marginal lappets, the pigment spot, 

 and the protuberances with nematocysts on the exumbrella. 



3. Turn the piece over and examine it under higher power 

 (100 diameters). Make a half page drawing showing the horse- 

 shoe bend of the circular canal, the ends of the radial 'canals, the 

 canals leading from the circular canal into the tentacles, the 

 canal leading into the tentaculocyst with two blind canals at 

 its base, the marginal lappets, the pigmented cupped eye, and 

 the statocyst at the end of the tentaculocyst. 



4. Transfer the piece onto a slide, add a drop of glycerine, 

 cover with a cover glass and examine the ectodermal covering 

 of the subumbrella under higher power (200 diameters). Make 

 a drawing showing the circular muscles and the nematocysts 

 scattered over the surface. 



5. Cut off another piece of the margin of the medusa with 

 scissors and put it on a slide with its exumbral surface upper- 



