63 
the vernal pulse, of the midsummer maximum of the chlorophyll- 
bearing Mastigophora, and of the autumnal-winter wave of Czlzata. 
The Protozoa, through the Mastigophora, share with the algz 
the synthetic function in the elaboration of food from inorganic or 
partially disorganized organic contents of the water. They utilize 
decaying organic matter as food, and are thus primary links in the 
cycle of food relations. Some of them feed upon bacteria, upon alge, 
or even upon other animals, and thus become secondary or tertiary 
links in the chain. 
MASTIGOPHORA. 
(Plates I. and II.) 
Average number, including, without duplication, both silk and 
filter-paper collections, 95,856,449. In the collections of 1897 
they were five times as abundant as a result, in part at least, of the 
extended low-water period, sewage contamination, and extension 
of high temperatures during the late autumn of that year (Pt. L., 
Pie ct.) 
The Mastigophora abound in every collection and occur at all 
seasons of the year. Four fifths of them occur, however, between 
the first of April and the last of September. They are predominant- 
ly chlorophyll-bearing organisms, and have their greatest numbers 
during the same season in which the land flora attains its growth. 
They spring into abundance with the opening buds of April, and van- 
ish from the plankton when frost cuts off the foliage in autumn. 
There are, it is true, some species, such as Synura, which grow 
luxuriantly at winter temperatures, but these are generally of the 
chrysomonad type, with yellowish or brownish chromoplasts. The 
bright green chlorophyll-bearing flagellates are in the main summer 
planktonts. Since water temperatures do not fall below 32°, the 
phytoplankton is exempt from this risk of destruction against which 
the land floramust provide. We find, accordingly, that the most of the 
Mastigophora are wont to occur in diminished numbers and irregu- 
larly in the plankton throughout the winter. This appears in the 
records of the more common species, and fuller examination would 
doubtless greatly increase the number which thus winter over in 
reduced numbers. 
I have already called attention to the fact that there are in 
1898-99 recurrent pulses in the Chlorophycee and Bacillariacee at 
