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 spiring, 

 constantly increasing from March until October, with average numbers per square 

 meter, by months, for the years 1915 and 1920, as follows: February-March, 6S5; 

 April, 501; May-June, 2,23S; 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. dengdtus 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 hall" separately, as follows: 



Average numbers per square meter, by months, counting only the stations of occurrence 



Locality 



February- 

 March 



Basin as a whole 



Basin eastoflongitude 68° W W. 



1,068 

 1,083 



April 



May-June 



656 

 811 



2,914 

 3,149 



August- 

 September 



8,963 

 6,752 



October 

 (only 1 sta- 

 tion) 



9,110 



Unfortunately, nothing can be 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 



