HYDROMEDUSAE 315 



adjoining the ring canal, about fifty or more, each with a single statolith. Colour: 

 Stomach, gonads, and basal bulbs pale yellow (in formalin or alcohol). Size: Umbrella 

 about 22 mm. in width and 14 mm. in height (largest specimen). 



The first collection contains about 150 specimens, taken in Stanley Harbour from 

 November 1898 to February 1899, showing a fine series from the early stages up to the 

 fully grown adult. In the second collection there are about forty-five specimens, like- 

 wise from Stanley Harbour, collected from 6 November 1901 to 27 March 1902; young 

 specimens were present during the whole of this period and adults were found from 

 26 December. 



Measurements of some of the larger specimens: diameter 14 mm., height 10, 11, 

 12 mm.; diameter 15 mm., height 13 mm.; diameter 17 mm., height 10, 13 mm.; 

 diameter 18 mm., height 11, 14, 15 mm.; diameter 19 mm., height 13 mm.; diameter 

 20 mm., height 12, 13, 14, 14, 15, 18 mm.; diameter 21 mm., height 15 mm.; diameter 

 22 mm., height 13, 14 mm. 



The umbrella of all the stages is very thick and solid ; its proportions vary very much, 

 but there is a distinct tendency to broaden as it grows. In the earliest stages observed, 

 i-i|mm. wide, it is bell-shaped and usually a little higher than wide; in the inter- 

 mediate stages it is frequently somewhat globular. In very early stages several nemato- 

 cysts are seen scattered over the exumbrella. The velum is very broad in the early 

 stages, but gradually becomes less conspicuous. 



The stomach in the early stages is fairly short, one-quarter to one-half the length of 

 the umbrella cavity, and has a quadrangular base, but in the adult the four radial canals 

 form a distinct cross over the base of the stomach (Plate XVIII, fig. 11). When expanded 

 the stomach is like a small globular or conical bag with thin walls, but when contracted it 

 becomes cross-shaped in transverse section (Plate XVIII, fig. 12). The mouth in the early 

 stages has four small, simple perradial lips, which increase in size as the medusa grows, 

 and its margin becomes folded. There is a band of nematocysts round the mouth rim. 



The gonads commence to develop when the umbrella is about 2 mm. in width, and 

 are then continuous with the stomach wall (Plate XVIII, fig. 9), just as in the Moerisiidae 

 and in Ostroiimovia among the Olindiidae, giving further evidence of the relationship 

 between these two families. The gonads gradually grow down the radial canals nearly 

 to the ring canal, and become separated from the stomach (Plate XVIII, fig. 1 1). At first 

 they form a narrow, simple band, which gradually becomes folded (Plate XVIII, fig. 8). 

 In the adult the gonads are divided by numerous deep transverse furrows, and the 

 ridges between the furrows become lobed (Plate XVIII, fig. 10). The gonads are not 

 divided in the median line on the lower side. 



When the diameter of the umbrella is 3-5 mm., the gonads are about one-quarter to 

 one-third the length of the radial canals and still adjacent to the stomach; diameter 

 5-6 mm., gonads about one-half to two-thirds the length of the radial canals, not 

 folded; diameter 8-10 mm., gonads about two-thirds to three-quarters the length of 

 the radial canals, slightly folded. The radial canals, and especially the ring canal, are 

 very broad in all stages. 



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