PLANKTON OP THE GULF OF MAINE 
369 
Although Pleurobrachia can hardly be classed as an important food supply for 
other animals, fish do prey on them more or less. In New England waters this applies 
especially to the spiny dogfish (p. 105). 
Alexander Agassiz, to whom we owe an excellent account of the development 
of Pleurobrachia, found its eggs in Massachusetts Bay late in July, in August, and 
in September, when, as he writes (1874, p. 359), “ the water round them is filled with 
eggs floating a few inches below the surface,” and when he took the earliest stages 
after hatching. This, with our own observations, makes it certain that Pleurobrachia 
is regularly endemic and breeds in large numbers in the Gulf of Maine, of which it is 
as characteristic an inhabitant as Calanus jinmarclricus or Sagitta elegans. But how 
many generations are produced there per year is not known. The older view was 
that there is only one, and that the product of eggs spawned in late summer and 
autumn live over winter, to mature and spawn in their own turn the following sum- 
mer. The presence of large Pleurobrachia in winter and spring as well as in mid- 
summer and autumn, together with the various sizes of the individuals which go to 
make up the different schools in different localities at any given season, makes it 
more probable that one generation succeeds another irregularly throughout the year. 
In spite of conclusive evidence to the contrary, assembled by recent students 
of ctenophores, Pleurobrachia has often been termed a northern, even an Arctic, 
form in its occurrence off the New England coast. I must therefore reiterate that 
this is not the case but that its regular range along the coasts of eastern North America 
extends southward to Chesapeake Bay; in fact, nearly to Cape Hatteras in the cold 
season, for I myself have found it plentiful in the waters of Pamlico Sound in 
winter. 
On both coasts of North America Pleurobrachia grows much larger in cool water 
(10° or colder) than in warm (Bigelow, 1915, p. 322; Esterly, 1914). Judging from 
the large size (upwards of 30 millimeters long) and local abundance of Pleurobrachia 
in the Gulf of Maine, the latter is as favorable an environment for it as are the colder 
waters off Newfoundland and Labrador; and if numbers of individuals present can 
be trusted as a criterion this applies equally to the coast water off New York and 
New Jersey, where rather smaller individuals are so abundant in some summers, for 
instance 1913, that they have been given a vernacular name (“sago”) by local 
fishermen 
Pleurobrachia is a creature of the upper strata of water. As Alexander Agassiz 
(1874, p. 359) remarked long ago, they come to the surface whenever it is smooth, 
at all times of day; “they are found in the greatest number between the hours of 9 
and 11 in the morning, and from 4 to 6 in the afternoon in the summer,” which is a 
common habit of this ctenophore in all parts of the gulf during summer and early 
autumn. In August, 1912, for example, we made our largest catches of Pleurobra- 
chia at the surface; but they sometimes lie deep throughout the day in midsummer 
and even in bright calm weather, as was the case on German Bank on August 12, 1913, 
when we found no Pleurobrachia on the surface at 10 to 11 a. m., although a haul 
from 40 meters yielded them in abundance. At other times of year this ctenophore 
occurs more regularly a few meters (say 20 to 30) down than shallower, as exemplified 
