PLANKTON OP THE WOODS HOLE REGION 
151 
of fire as it swayed back and forth in the current. As the amphipods are positively 
phototropic, many, no doubt, are attracted by the light and are drawn into the net. 
Another factor as well may influence these collections which were always foimd more 
abundant at night. Experiments have shown that many amphipods rise to the 
surface at night and go down in the daylight. If this is true for many of the species, 
we should expect to find them more abundant in surface collections taken in the 
evening. How much effect this really has upon the plankton hauls I do not know, 
but I offer it as a possible explanation. I found no conditions in winter that could 
have resulted from such causes. Possibly the evening migrations do not take place 
during the cold season. 
The following amphipods were taken in smiace collections diu"ing 1922 and 
1923: 
Euthemisto bispinosa (Bceck). 
Tryphosa pinquis (Boeck). 
Paraphoxus spinosus, Holmes. 
Ampelisca spinipes. Boeck. 
A. macrocephala, Lilljeborg. 
A. compressa, Holmes. 
Byblis serrata, Smith. 
Stenothoe cypris, Holmes. 
Monoculodes edwardsi, Holmes. 
Calliopius laeviusculus (Kroyer). 
Pontogenia inermis (Kroyer) . 
Batea secunda, Holmes. 
Gammarus locusta (Linnseus). 
Carinogammarus mucronatus (Say). 
Elasmopus laevis (Smith). 
Ptilocheirus pinquis, Stimpson. 
Amphithoe rubricata (Montagu). 
A. longimana, Smith. 
Jassa marmorata, Holmes. 
Grubia compta (Smith). 
Ericthonius rubricornis, Stimpson. 
Corophium cylindricum (Say). 
Unciola irrorata. Say. 
Synchelidium sp. 
Caprella linearis, Linnseus. 
C. geometrica, Say. 
G. annulatus. Smith. 
The Isopoda, with the exception of certain parasites, do not normally form a 
part of the plankton. They are most abimdant in surface collections in summer. 
This is because mmibers of Idothea and alUed genera are found on floating Sargassum 
and Fucus, which, when carried into the nets or forced by them, often deposit many 
of their passengers. In winter this condition does not exist and few species are taken. 
On one occasion in the spring of 1900 many adult Cirolana concharum appeared in 
the tow. No doubt these were floating on a piece of wood or a dead fish which 
may have been carried into the net. 
The most interesting by far of the isopods taken during the summer were four 
minute species of the family Bopyridfe, which are parasitic on copepods. These 
occurred in large numbers at certain times. Two species were foimd on Acartia 
tonsa, one on Centropages typicus, and one on Lahidocera xstiva. They were most 
abxmdant from July to October, one specimen appearing unattached on December 20. 
None of the winter copepods seemed to be infested. No species have been recorded 
from this coast, and as a paper on these forms, now in the course of publication in 
England, is not yet completed, it was decided to wait for it before attempting to 
identify these isopods. 
The following species were taken in 1922-23: 
Idothea baltica (Pallas). 
I. phosphorea, Harger. 
I. metallica, Bosc. 
Edotea triloba (Say). 
Circolana concharum (Stimpson) . 
Tanais cavolinii, Milne Edwards. 
Chiridotea cseca (Say). 
Leptochelia savignyi (Kroyer). 
Erichsonella filif ormis (Say) . 
Family Bopyridse, four species. 
