IOWA ACADEMY OF SCIENCES. 31 



being brilliantly phosphorescent, Gorr/onida', Aiitipathklcr, 

 Hi/droida and msknyje/h/-^fishes. Among the Protzoa, the noctiluca 

 is perhaps the most widely diffused and numerically the 

 greatest of all. 



It should be remembered in this connection that it is alto- 

 gether probable that the phosphorescence of deep-water forms, 

 e\en where present, is only exceptionally discovered. While 

 dredging operations are under way the work is usually done 

 by daylight and the specimens are sorted and cared for as 

 quickly as possible, only a small portion from considerable 

 depths being alive when brought to the surface, and only a 

 fraction of these being kept alive for nocturnal observations. 



Under these circumstances, the occurrence of phosphor- 

 escence would be, as I have said, only exceptionally noted, 

 even were it abundantly present in the forms studied. When 

 we consider the above list of phosphorescent forms that 

 have been recorded in spite of the conditions just referred to, 

 it will be conceded that the actual amount of this light must be 

 far greater than the face of the record shows. 



It is well to bear in mind also, in this connection, that many 

 of these phosphorescent forms, especially among the fixed 

 coclenterates, are aggregated together in masses on the sea 

 bottom: No one can have had much experience in dredging in 

 rich localities without noticing this. Agassiz speaks of 

 ' 'forests of gorgonians which become luminous by disturbances 

 due to currents or other movements, '' * and I have frequently 

 been surprised, when dredging on the Pourtales Plateau, at 

 the immense quantities of echinoderms and cut'lenterates 

 secured at a single haul, indicating a profusion of life on 

 definite areas of the sea bottom. 



Taking the above facts into consideration, it is safe to say 

 that phosphorescent light is a very characteristic and widely 

 spread phenomenon which must enter into our discussion of 

 the physical features of the deep sea. 



It now becomes necessary to consider veiy briefly the 

 nature and extent of organs for the perception of light and 

 color with which the dwellers of the deep sea are endowed. 



On this point Agassiz has the following statement: f 



' 'We should not forget on the one hand that blind Crustacea 

 and other marine invertebrates without eyes, or with rudi- 

 mentary organs of vision, have been dredged from a depth of 



*'• Three Cruises of the Blake," p. 308. 

 + •• Three Cruises of tlie Blake," p. 307. 



