1892] The Problem of Marine Biology. 805 
as well as the transparent, newly-hatched fry must be men- 
tioned. Prof. Hensen hopes to get an idea of the approximate 
number of fish of a given species in a certain area, computing 
the number of eggs and fry of that species within that area. 
The phenomenon of marine phosphorescence is very widely 
known with admiration and wonder. . Its cause is chiefly or 
solely bound up with organic life. The majority of pelagic 
animals display the phosphorescent light in different degrees. 
- In some the entire living animal is brighly luminous; in other 
the light is limited to special organs. But much of the phos- 
phorescence of the ocean appears to be caused by the fragments 
of dead organisms, and is connected with the presence of bac- 
teria. 
Since many chlorophyll-bearing organisms are found at 
depths unpenetrated by sunlight it has been suggested that 
the light necessary for their growth is furnished by the phos- 
phorescent organisms. 
The composition of the Plankton is exceedingly irregular, 
both in qualitative and in quantitative relations ; its distribu- 
tion in the ocean is also very irregular, both in time and in 
place. The variations occur near the shore as well as far 
out at sea. Very often the greater part of the mass 
of Plankton is made up of organisms belonging to a single 
group. Sometimes unicellular alge make up nearly the whole 
bulk, at another meduse, siphonophores or ctenophores ; ; 
indeed; almost any group of marine organisms may occur in 
such quantities as to compose more than one-half of the total 
bulk of the Plankton, at that time and place. The funda- 
mental causes of variation in the quantity and quality of the 
Plankton appears to be conditioned by time, climate and cur- 
rents. 
. Temporal Differences—For a satisfactory determination of 
these more complete observations are needed. Reliable data 
can be furnished by the observations at the numerous marine 
laboratories and zoological stations now springing up in differ- 
ent parts of the world. The causes which underlie these 
yearly, monthly, daily and hourly variations are manifold ; in 
part meteorological, in part biological. They are comparable 
