222 THE MEDUSAE. 



food supply, and the like, which are associated with every coast line, no 

 matter how abrupt it may be. 



I cannot pass over without mention the extraordinary richness of the 

 Humboldt Current in pelagic life of all kinds ; a richness which has already 

 been noted in the account of the general oceanographic features of the 

 Eastern Tropical Pacific by its leader, who speaks of " such masses of Sal- 

 pae, of Cytaeis, or Cymbulia, or swarms of other pelagic animals as to 

 make a thick soup" (A. Agassiz, : 06, p. 15), and of enormous quantities of 

 copepods, schizopods, Doliolum, and Medusae. Nor can I omit to recall the 

 discovery, immediately to the west and southwest of the Current, of an 

 area as barren in all forms of life, bottom as well as pelagic, as the latter 

 is rich. Thus " As soon as we ran outside of this [the Humboldt Current] 

 the character of the surface fauna changed ; it became less and less abun- 

 dant as we made our way to Easter Island, the western half of the line 

 from Callao becoming gradually barren" (A. Agassiz, : 06, p. 9). On enter- 

 ing the Current again from the barren area the reverse change was equally 

 striking. Thus, to quote further: — " The pelagic and intermediate fauna 

 from Easter Island to 12° south latitude was very poor, and the serial 

 temperatures show that we were outside and to the westward of the 

 great Humboldt current. But near the 12th degree of southern latitude 

 a sudden change took place ; the pelagic and intermediate fauna became 

 quite abundant again and soon fully as rich as at any time in the Humboldt 

 current. There was also a marked change in the temperature of the water 

 as indicated by the serials, showing that from the 12th degree of southern 

 latitude to the Galapagos we were cutting across the western part of the 

 Humboldt current" (A. Agassiz, : 06, p. 9). 



The surface holoplanktonic Medusae in their quantitative distribution 

 well illustrate the general conditions thus outlined. Several species of 

 this group were so regularly taken that the Expedition may be said to 

 have given a comprehensive survey of their occurrence in the region 

 traversed, and the captures of four of these, which may be taken as typical 

 of the group, l/irtope tetraphylla, Rhopalonema velatum, Aglaura hemistoma, 

 and Cytaeis vulgaris, are graphically indicated on the chart, Plate 47. All 

 of these species ii.timtimI on all the lines, both within the Current and in the 

 barren area, while all but Cytaeis vulgaris were likewise taken off the west 

 ' of Mexico, and in the Gulf of Panama. I should mention that the 

 small number of records on the passage from Manga Reva to Acapulco is due 



