SCYPHOMEDUSAE 375 



often impossible to say with any certainty whether a specimen belonged to Broch's 

 groups III or IV. Most probably the greater part of the exumbrella and subumbrella in 

 dark specimens is covered with pigment, with the exception only of the apical part of 

 the central disc. Everywhere there are spots, traces of pigment in the furrows of the 

 central disc, in the coronal furrow, between the pedalia and in their furrows, in 

 the tentacle muscles, and in the subtentacular pockets. The stomach and the peripheral 

 parts of the gastro-vascular system and the subtentacular pockets are mostly very deeply 

 pigmented. In the darker specimens the largest part of the subumbrella is covered with 

 a dark reddish brown epithelium hanging down here and there in small pieces from the 

 surface. 



In the present series of eighty-five specimens the bathymetrical distribution of which 

 could be established by closing net hauls (see Table VII), nine belong to stage I, none 

 to stage II, forty-eight to stage III and twenty-eight to stage IV. 



According to Broch's statements the very dark specimens of stages III and IV are 

 never found above the 750 m. In the Discovery material the Antarctic specimens from 

 Sts. 592, 595, 563, WS 552F, caught between 450 and 124 m., are very dark, and all 

 belong to stage IV. Off the African coast very dark specimens of the bairdi and wyvillei 

 type were found at the surface (St. 270, Elephant Bay, and St. loi , west of Cape of Good 

 Hope). There were also found here dark and lighter specimens of three different stages 

 of pigmentation in one and the same haul, e.g. at St. 407, and in many other catches with 

 open nets dark and light specimens are picked up together. On the other hand a very 

 light specimen was caught at a great depth (St. 401, 1250-1300 m.). As seen from 

 Table VI the bulk of the dark specimens were caught in an intermediate layer between 

 650 and 1500 m. Only occasionally have some been found in more superficial layers or in 

 still deeper water. This is not in accordance with Broch's table 9. Here the lighter stages 

 live in more superficial layers and have their maximum at 500-750 m. The deeply pig- 

 mented specimens live only in water deeper than 750 m. The single specimen of Atolla 

 wyvillei caught by the 'Michael Sars' was taken at a depth of 1500m. The maximum 

 of Broch's specimens of bairdi lay at 1000 m. Still I agree with Broch that the pigmenta- 

 tion generally increases with the depth. That Table VII does not show this rule is due 

 to the fact that the hauls from Antarctic waters and Elephant Bay are here included. 

 We know that in polar regions the distribution of deep-water organisms is universal, 

 and that on the West African coast up welling cold-water currents drive abyssal forms 

 upwards to higher strata. 



The RING MUSCLE in most cases, particularly in deeply pigmented specimens, where 

 the pigment is partly fallen off, is of a strange greenish yellow colour, with a tint of opal 

 or mother-of-pearl, or is of a vivid yellowish colour. On a specimen from St. WS 263 

 I found dark brown radial stripes on the greenish ring muscle. 



Geographical distribution (see Fig. 6). Atolla is found along the whole route of 

 the ' Discovery ' from the Cape Verde Islands and the Gulf of Guinea, along the coast 

 of West Africa to the Antarctic regions. Most specimens were caught in a broad zone 



