156 DISCOVERY REPORTS 



speed of hauling and the occurrence of swarms are not known precisely. As far as ' Manihine ' records 

 are concerned it is assumed that an open 1 m. stramin net was hauled obliquely from either 183 or 

 366 m. to the surface whilst the ship went slowly ahead for about 100 metres. 



Abundance of Abylopsis tetragona per unit volume of zvater 

 1. 'Thor', Mediterranean, western basin (Bigelow & Sears, 1937). Mean frequency of specimens, 

 at the level of maximum abundance, at Stations where the species occurred : 



2. ' Meteor ', warm tropical Atlantic. Frequency at several levels, calculated from Bigelow & Sears's 

 tables (based on those of Leloup & Hentschel, 1935): 



3. 'Manihine', Red Sea, off Port Sudan, 16/17 January 1951. (T. ° C. estimated at 21-5-22; 

 equivalent to a late June surface temperature at Villefranche, West Mediterranean) : 



It appears that Port Sudan would be a favourable spot at which to attempt to observe the species 

 throughout its life cycle, an objective that has not so far been achieved. The importance of this is 

 to ascertain whether the small anterior nectophore is the primary nectophore or a secondary hetero- 

 morphous one. Haeckel's attempt at Lanzerote in 1867 failed. So also did my own at Villefranche 

 in 1950, where, at that time, there were never more than two or three ripe gonophores available on 

 odd days, and then generally one sex or the other and not both at once. 



Text-fig. 83 illustrates the arrangement of the two hydroecial folds, for comparison with the 

 arrangement in Abyla spp. A distinctive character is that the broad, left-hand fold, the free edge of 

 which Moser called the left, pseudo-dorsal ridge, is held in place at one point between two parts of the 

 right-hand fold, i.e. between a mamma-like structure and the comb or' Leiste ', at a position just proximal 

 to the terminal parting of the two folds. Moser's figure (1925, pi. xx, fig. 4) and her description (p. 330) 

 does not make this clear. It should be remembered that owing to her fantastic ' Urmedusentheorie ' 

 she called the morphological dorsal side of a posterior nectophore ' ventral '. The ' Leiste ' or comb, which 

 Moser described as arising from the 'dorsal' wall of the nectosac should, I believe, properly be 

 considered as part of the free, ventral margin of the right hydroecial fold, as can be seen at any rate 

 proximally in the apophysis or portion of the posterior nectophore that is enclosed in the hydroecium 



