38 
BULLETIN OF THE BUREAU OF FISHERIES 
place to a rich Peridinian flora in summer, which is succeeded in turn by the limited 
flowering of diatoms in autumn, as described in the chapter devoted to the phyto- 
plankton (p. 383). 
No such seasonal alternation of dominance by one or other group takes place 
among the planktonic animals of the gulf, however, though there is a very pro- 
nounced oscillation in the total amount of zooplankton present there at different 
times of year and in the abundance of its several members relative to one another. 
Thus, we have never failed to find the Calanus community dominating the pelagic 
fauna generally in the southwest part of the gulf, whether our trips thither were 
made in the heat of summer, the cold of winter, in autumn, or in spring. Neverthe- 
less, even in this region the varying seasons of reproduction of different animals, 
which determine the presence or absence of their larvae and the abundance or scarcity 
of the adults, with the local irregularities of distribution that always obtain for the 
larger pelagic forms, added to the general ebb and flow in the abundance of the 
zooplanktonic community as a whole, cause such variations from month to month as 
appear in the following lists of the more abundant species in tow-net catches made 
at the mouth of Massachusetts Bay in spring, summer, autumn, and winter. The 
case is made still more complex by sporadic fluctuations in the abundance of one 
species or anotiier, for which we are not yet able to account. 
Tow-net catches at the mouth of Massachusetts Bay 
[D. dominating the plankton; X, occurred] 
Mar. 1, 
1920, 
station 
20050, 
75-0 
meters 
Apr. 9, 
1920, 
station 
20090, 
60-0 
meters 
May 4, 
1920, 
station 
20120, 
40-0 
meters 
July 9, 
1916, 
station 
10341, 
0 and 80-0 
meters 
Oct. 31, 
1916, 
station 
10399, 
60-0 
meters 
Feb. 13, 
1913, 
station 
10053, 
20-0 
meters 
Cod eggs 
X 
Haddock eggs 
X 
Cod or haddock eggs 
x 
X 
Silver hake (Merluccious) eggs 
X 
Silver hake (Merluccius) larvae 
X 
Butterfish (Poronotus) eggs 
X 
Plaice (Hippoglossoides) eggs 
x 
X 
Plaice (Hippoglossoides) larvae 
x 
X 
Dab (Limanda) larvaj 
X 
Witch (Glyptocephalus) larvae 
X 
Oiko pleura 
X 
X 
Decapod larvae 
X 
Thysanoessa inermis 
X 
Thysanoessa raschii 
X 
Meganyctiphanes norvegica 
X 
Euphausiid larvae 
x 
Euthemisto compressa 
x 
X 
Euthemisto bispinosa 
X 
X 
Calanus finmarchicus 
D 
D 
D 
D 
D 
D 
Calanus hyperboreus 
x 
Pseudocalanus elongatus 
X 
X 
X 
X 
Metridia lucens 
X 
X 
X 
Anomalocera pattersoni 
X 
Euchaeta norvegica 
X 
X 
D 
Centro pages hamatus 
X 
X 
Copepods, juvenile 
X 
X 
D 
X 
Copepod nauplii 1 
D 
X 
Sagitta elegans 
D 
X 
X 
D 
X 
X 
Sagitta serratodentata 
X 
Tomopteris catherina 
X 
X 
Limacina retro versa.. 
X 
X 
X 
x 
x 
Aglantha digitale 
X 
X 
X 
X 
X 
