kofoid: mutations in ceratium. 249 



hydrographic factors in common. They were both taken in regions 

 where hydrographic contrasts were noticeable. 



The heteromorphic chain shown in plates 1-3 was taken at Station 

 4737, 500 miles N. E. of Manga Reva in the southern margin of the 

 great eddy that lies in 'the angle between the South Equatorial and the 

 Humboldt current. The station was located over the depression be- 

 tween the Albatross Plateau and that from which the Paumotu Archi- 

 pelago rises, a depression blocked to an unknown extent to the south 

 by Pitcairn and other scattered islets. (See Mr. Agassiz's (1906) Report 

 of the Expedition, plates 1 and 2.) Across this gap as the " Albatross " 

 approached Manga Reva there was a rapid decline in surface tem- 

 peratures from 81.5° to 77.5°. The distribution of surface temperatures 

 elsewhere in this region suggests the existence (see Agassiz, 1906, plate 

 3 a) of a belt extending eastward from Manga Reva and skirting the 

 southern edge of the Albatross Plateau in which there is a change in 

 surface temperature, 4.5° in 4° of latitude, which is relatively rapid as 

 compared with those in the region of the adjacent eddy. An area of 

 higher specific gravity (1.0260 as compared with 1.0252-1.0256. See 

 Agassiz, 1906, plate 3 b) extends in a similar direction. The specific gi'avity 

 of the water at tliis station is higher than that upon either side for some 

 distance. Temperature sections at adjacent stations (see Agassiz, 1906, 

 plate 5) to a depth of 800 fathoms show noticeable irregularities but no 

 extreme conditions. An unusually large amount of dead and moribund 

 material (see Agassiz, 1906, p. 18) occurred in the plankton of this locality. 

 The possibility of an up welling from deeper layers in the neighborhood 

 is thus suggested in view of the configuration of the bottom and the 

 hydrographic conditions above noted. We may conclude that this 

 heteromorphic chain occurred in a region offering possibilities of 

 environmental contrasts. 



The second heteromorphic chain (plate 4, fig. 4) Avas taken at Sta- 

 tion 4711, about 500 miles S. W. of Chatham Island and near the outer 

 edge of the great Humboldt Current as it turns westward in the South 

 Equatorial. The temperature conditions at this and an adjacent Sta- 

 tion, 4713, were extraordinary (see Agassiz, 1906, p. 21, plate 8) in the 

 rapidity with which the water became colder within the short distance of 

 50 fathoms from the surface. The temperatures at this station at the 

 surface, 25, 50, 100, 200, 300, 400, 600, and 800 fathoms, were 75.3°, 

 73.8°, 59.5°, 54.9°, 51.1°, 45.6°, 43.4°, 39.2°, and 37.4°, a decrease in 

 the first 50 fathoms of 15.8°, and in 100 fathoms of 20.4.° The change is 

 most rapid between 25 and 50 fathoms, where it amounts to a difference 



