IOWA ACADEMY OF SCIENCES. 
31 
being brilliantly phosphorescent, Gorgonida^ Antvpathidce, 
Hydroida and m?bn.j jelly-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, 
even 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 
coelenterates, 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 coelenterates 
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 very briefiy 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. 
t ‘‘ Three Cruises of the Blake,” p. 307. 
