PLANKTON OF THE WOODS HOLE REGION ¥ 149 
ARTHROSTRACA 
Twenty-seven species of Amphipoda were taken in surface hauls during the 
past year. But one of these (Luthemisto bispinosa), belongs to the pelagic family 
Hyperiide. Young specimens were found on five occasions in January. The adults, 
which are often parasitic in Aurelia and Cyanea, are usually seen after southerly 
winds, when the medusz are blown into the harbor. All other amphipods belong to 
the benthos. During the breeding season, however, some species swim at the sur- 
face, both in daytime and at night, and are often taken in the tow in large numbers. 
Thus, the bottom forms may be divided into three groups, viz: (1) Those that 
swim during the breeding season, (2) those that are carried by the currents, and 
(3) those forms that for some reason other than the breeding season are attracted 
to the surface. 
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Fic. 50.—Occurrence of amphipods in Fic. 51.—Occurrence of amphipods in surface collections of 1923. Free- 
surface collections from June to De- swimming period during breeding season. , Calliopius lxvius- 
cember, 1922. Free-swimming pe- culus; —-ese—, C. lzviusculus (young); --------, , Monoculodes 
riod during the breeding season. edwardsi; —-—-——, Batea secunda; —.» —, Gammarus annulatus 
. Batea secunda; ——ec.—, 
Monoculodes edwardsi; —« -—, Gam- 
marus annulatus; ------=-<, , Callio- 
pius leviusculus; —-—, Stenothoé 
cypris 
In the first group there are two very conspicuous summer breeders. These 
can be found in Figure 52, designated by a long line. Certain forms, like Caprella, 
appear to have such a season, but this is caused by another condition. They live 
on hydroids, and as many of these are found floating after every strong wind the 
amphipods attached to them will float long after other forms have sunk again to 
the bottom. Of the summer forms Batea secunda and Stenothoé cypris are very 
noticeable. At times hundreds of specimens were taken in a single haul, many of 
the females carrying eggs or early embryos. 
On November 6, 1922, Monoculodes edwardsi started breeding (fig. 50). Many 
were taken throughout December and on a few occasions in January, the last 
occurring on January 21. About the middle of December two other species (Cal- 
hopius leviusculus and Gammarus annulatus) suddenly appeared in abundance. 
The former often swarmed at the surface in large numbers, and individuals could 
