MEDUSAE. 55 



the gonacls develop the baud becomes siimously folded and broadens. In the young 

 adult the baud is about 4 mm. iu width aud somewhat semicircular in shape. 

 There is no sub-genital cavity as in Aurelia aurita. The gonacls protrude from the 

 stomach and hang down from the sub-umbrella like the gonads of a Chrysaora. 

 In the meta-ephyra stage the genital sacs have the appearance of simple sac-like 

 enlargements, with very thin walls ; on the wall of the stomach inside are situated two 

 rows of gastric filaments and the embryonic genital band. By the time the gonads 

 have reached maturity the genital sacs have become lobated (Plate VI., fig. 5). 

 Internally the proximal end of the sac is covered with numerous gastric filaments, and 

 its distal end or bottom holds the gonads, which are now arranged in more complicated 

 and somewhat irregular folds. 



The tentacles are very much laterally compressed, especially in the basal portion, 

 but the distal portion is more round and tapers off to a slender point. Along the 

 whole length of the tentacle, on the inner side, runs a band or ridge, which is closely 

 studded with clusters of nematocysts. The outer side of the tentacle is smooth and 

 free from clusters of nematocysts (Plate VI., fig. 6). The tentacles are hollow 

 throughout their whole length, a flat tube-like cavity running close to the inner edge. 

 They are apparently in a semi-contracted condition, and the tube-like cavity is 

 contracted into a series of transverse folds, which, when viewed from the outer edge 

 of the tentacle, have the appearance of a series of rings. The folding or wrinkling 

 is present in all fully-grown tentacles, and is sufficiently conspicuous to be noticed 

 by the naked eye. 



In the adult there are normally sixteen sense organs, alternating with sixteen 

 tentacles. The rhopalium, or tentaculocyst, is not well protected in this Medusa 

 neither by lying back in a groove nor by a covering formed by the marginal lobes. 

 It is situated on the wall of the niche formed by the marginal lobes, and points 

 upwards towards the aboral side of the umbrella. The rhopaliar canal, which leads 

 from the circular canal to the sense organ, is broad and flat in the adult. Over the 

 rhopaliar canal and on the surface of the umbrella is situated a small patch of darkly 

 coloured cells, in the midst of which there is generally a slight depression forming 

 the dorsal sensory pit. The pit has the appearance of being in a rather rudimentary 

 condition and is occasionally absent. 



Although the marginal lobes are more or less torn, there are no indications of 

 any further increase in number, beyond the original thirty-two of the ephyra stage, 

 by subsequent division. The ex-umbrellar side of the lobes is covered with numerous 

 warts containing nematocysts. The lobes show a slight variation in shape, and fill 

 up the space between the sense organs and the tentacles. As these are not always at 

 equal distances apart, some of the lobes are broader than others. 



Vanhb'ffen's description of the adult is based upon a large fragment of the 

 marginal part of the umbrella, and Maas had only one quadrant of an umbrella to work 

 upon. Vanhoffen describes and clearly figures tentacular lobes on the margin of the 



