THE SIPHONOPHOEA. 



D. appendiculata is the most abundant siphonophore in the collection, 

 rences were as follows : — 



845 



Its occur- 



Fortunately the anterior and posterior nectophores are all in such, good condition as 

 to be recognized readily. But many of the eudoxids are very much battered. Only 

 those which could be identified certainly are listed above; there are a considerable 

 number in addition which may belong to this same species. 



D. appendiculata has long been known to be a widely distributed form, not only 

 belonging to the epiplankton, but living at very considerable depths (1300 metres, Chun, 

 1887; 1000 metres, Bedot, 1904). Indeed, it is perhaps the most nearly universal 

 of all siphonophores. The captures show that its eudoxid is commonest on the surface, 

 but that in the Bay of Biscay the polygastric generation, on tlie contrary, is most 

 abundant in the zone between 100 and 25 fathoms. The scarcity of the adult on the 

 surface is surprising, in view of the fact that it has been so commonly taken there in 

 other localities, both tropical and temperate. Below 100 fathoms both adult and 

 eiidoxid are rare ; but the excellent condition of the specimens of both forms, which were 

 taken in the closing-net between 500 and 400 fathoms, indicates that they were alive at 

 that depth, and not merely corpses on their way to the bottom. 



Its vertical range in the region now under consideration parallels that of Aglantha 

 among the Medusae (Browne, 1906, p. 174), a genus most common between 100 and 

 50 fathoms, though occurring in lesser numbers at much greater depths. 



D. appendiculata, like Nausithoe punctata among Scyphomedusoe, passes through a 

 wide range of temperature in its distribution, both vertical and horizontal. The evidence 

 of the present collection would suggest, for the polygastric generation, an optimum of 

 50°-60°r. But it occurs commonly on the surface in the tropical regions of all three 

 great oceans, in temperatures of from 70°-78°. The most northerly record which can 



SECOND SERIES. — ZOOLOGT, VOL. X. 55 



