SYSTEMATIC AND BIOLOGICAL ACCOUNT 83 



canal, the somatocyst, running from end to end. It lies just underneath the dorsal wall of the 

 hydroecium, except for the upper 5 mm. where it leaves the hydroecial wall and runs deeper in the 

 mesogloea. In the middle region of the specimen the hydroecium is deepest, and the longitudinal 

 canal has a corresponding bend, as in the better known Rosacea. Just at this point, and at the base 

 of the primary gastrozooid, is an ovate structure found also in post-larvae of R. plicata, R. cymbiformis 

 and Hippopodius hippopus. It is similar to the ' central organ ' found in the aboral end of some Prayid 

 eudoxids. It may act as a food reservoir or perhaps control density. 



The dorsal and ventral canals of the nectosac arise independently, one at each end of the nectosac, 

 and the lateral ones form a pair in the middle, as in the special swimming bell of the eudoxid. The 

 lower edge of the nectosac is distinctly undercut. The structure of the tentacle of the polygastric 

 specimen has not been well preserved, and the nature of the tentilla has not yet been elucidated. 



Study of a well-preserved eudoxid from 'Discovery' Station 287 (800-1000 m.) off the west coast 

 of Africa enables me generally to confirm Bigelow's (1931) account, and to add a little to it. The 

 two longitudinal hydroecial canals which arise as in Nectopyramis thetis, one on each side of the central 

 organ, join one another distally as in the type, though in another specimen from ' Discovery ' Station 

 100 (2500-2000 m.) west from Cape Town they do not. There is a ' central organ ' (Leloup's ' formation 

 speciale ') very similar to that in N. thetis, with a loop of the canal system — the semicircular bracteal 

 canal — running round the ventral side. The central-organ sac has probably burst, so that its junction 

 with the pedicular canal of the special nectophore 1 cannot be seen, but this pedicular canal arises in 

 approximately the same place as in N. thetis. The chief difference between the eudoxids of Nectopyramis 

 nutans and Nectopyramis thetis is that in N. thetis there have grown out a ventral and two dorso-lateral 

 processes of the bract, each served by a branch of the canal system. The tentilla of the eudoxid of 

 Nectopyramis nutans; viewed in situ, resembles those of Nectopyramis thetis and differ very markedly 

 from those of N. diomedeae. 



The relationship of this species have been dealt with above. 



Nectopyramis diomedeae Bigelow, 191 ib. (Plate V, figs. 2-3.) 



Only three polygastric and eight eudoxid specimens have ever been recorded, all from the Eastern 

 Tropical Pacific (Bigelow, 191 1 b, 193 1). I can now report that the species occurs also in the Atlantic, 

 where Beebe took seven polygastric and twelve eudoxid specimens off Bermuda. The specimens noted 

 in my list of Siphonophora taken by Beebe in 193 1 {Nectopyramis sp.nov.?) belong to the species 

 N. diomedeae. 'Discovery II' took two more polygastric specimens in the South Indian Ocean, in 

 32 lat., at Stations 1749 and 1755 ; two more off South-east Africa at Stations 1567 and 1568 ; and two 

 further polygastric specimens off East Africa at Stations 1585 and 1587. 'Discovery II ' took eudoxids 

 in the South Atlantic at seven stations between Station 679 at 26 S. lat. and Station 1555 at 39 S. lat. ; 

 and again at Station 1999 (64 S.) between South Georgia and the Ice Edge. 



From the records so far available I estimate that the species lives at a depth of from 650 to 1600 m. 

 or a little more. The polygastric stage has been taken, so far as we know at present, in only one closing 

 net haul (1060-600 m.) ; the eudoxid in eight, varying in depth between 625-675 m. and 1500-2000 m. 

 Beebe's seven hauls were open hauls to the surface after long horizontal hauls. His deepest net 

 (1829 m -) contained a polygastric specimen when it came to the surface, as did his 1646-m. net, but 

 there must be some doubt about the depth at which the captured specimens were living. 



Polygastric stage. There is the usual Prayid plan of a median longitudinal canal (Text-fig. 39 A, 

 C.med.long.) that passes round the dorsal side of the hydroecium. Below, it gives off the pedicular 



1 The special nectophore bears a manubrium and eggs, and is therefore a gonophore. The second gonophore probably 

 remains in a reduced condition as far as its general shape and subumbrella are concerned. 



