PLANKTON OF THE WOODS HOLE REGION 
135 
taken on July 18, although the numbers had been very small since June 20. In 
August, 1923, large numbers of small Sagittse of the spring brood were taken off No 
Man's Land in deep water. 
Many species of Platyhelminthes and Nemathelminthes have been recorded from 
surface collections, but these have been accidental in occurrence and, with the 
exception of certain early larvse, do not form a part of the littoral plankton. Most 
members of the phylum, excluding internal parasites, live among the marine plants 
Fig. 35. — Occurrence of Sagitia elegam in surface collections during successive years. Broken 
lines indicate scattering occurrence 
and detritus on muddy bottoms or on piles. Some forms like the rotifers, of which 
a few marine genera occur at Woods Hole, swim about freely, but even these are not 
a part of the open-water plankton. Only one rotifer (Synchaeta triopthalma Lauter- 
born) was observed during the past year, and this was seen but once. 
Often in summer planarians appeared, but no attempt was made to identify them. 
One species, however {Microstomum davenporti Graff), was taken in the harbor on 
