PLANKTON OF THE GULF OF MAINE 
281 
the vertical hauls for 1915 and 1920 (tables, pp. 297, 299) point to a greater absolute 
abundance over the area as a whole in late summer and autumn than in early spring, 
constantly increasing from March until October, with average numbers per square 
meter, by months, for the years 1915 and 1920, as follows: February-March, 685; 
April, 501; May-June, 2,238; August-September, 5,723; and October, 8,456. 
If the year 1913 be included in the calculation (Bigelow, 1915, table, p. 286), 
the August average would mount to 19,834, making this the seasonal maximum; 
but the possibility of an annual as well as a seasonal fluctuation must always be 
kept in mind. 
The seasonal cycle for 1915 and 1920 in the coastal zone between Cape Cod and 
Grand Manan paralleled the figures just given for the gulf as a whole, with the 
average numbers of P. elongatus augmenting from about 300 per square meter in 
March-April, to 2,124 for May-June (or 1,699, if the stations where it failed as well 
as those where it occurred are counted), 2,819 or 3,947 for August-September, and 
7,622 or 8,710 for October, depending on which basis of calculation be employed. 
The vertical hauls in the deeper parts of the gulf show a similar seasonal augmenta- 
tion from early spring to September, whether for the basin as a whole or for its 
eastern half separately, as follows: 
Average numbers per square meter, by months, counting only the stations of occurrence 
Locality 
February- 
March 
April 
May-June 
August- 
September 
October 
(only 1 sta- 
tion) 
1, 068 
1,083 
656 
2,914 
8, 963 
6,752 
9,110 
811 
3,149 
Unfortunately, nothing can he said as to seasonal fluctuations in the abundance 
of P. elongatus as distinguished from its frequency on Georges Bank or outside the 
continental edge, no vertical hauls being available thence for summer. 
Breeding habits . — In the northeastern Atlantic sexually adult specimens of both 
sexes have been reported repeatedly at various dates between April and September (for 
a summary see With, 1915), and since Willey (1919) describes females with eggs and 
attached spermatophores from the Gulf of St. Lawrence for August, the breeding 
season for Pseudocalanus might be expected to fall in late spring and through the 
summer in the Gulf of Maine. Dr. C. B. Wilson writes, in a letter: 
In this connection it is of interest to report that although the present collection includes speci- 
mens of this species taken in every month of the year except November, not a single specimen 
was observed with eggs. 
However, as he points out, Sars’s (1903, p. 21) discovery that the ovisac is so 
very fragile that it becomes detached at the slightest touch “readily explains Willey’s 
(1919) statement that the ovisacs of all the females were ruptured, and the fact 
that no females with eggs were found in the present collection.” 
Next to the actual discovery of egg-bearing females, the constant presence of this 
species in the gulf, its universal distribution and considerable abundance there, and 
the unmistakable seasonal cycle in its abundance are the strongest evidence that it is 
