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in the data here offered to indicate any tendency on the part of P. elongatus to keep to 
the deepest levels, nor can I offer any evidence of diurnal vertical migration on its part, 
though this is so common a phenomenon among copepods that more detailed study 
of the occurrence of the species is likely to show it in some degree. 
Seasonal cycle . — Pseudocalanus can not be described as definitely seasonal any- 
where within the gulf. This appears both from the percentages of stations at 
which it has been taken in different months, the variation from month to month 
being no greater than the chances of the hauls, and from the distributional chart 
(fig. 83), which proves Pseudocalanus present in all parts of the gulf both in the 
summer-autumn and in the winter-spring seasons. 50 However, if the records be 
considered by locality, the following regional differences appear: In the coastwise 
zone out to the 100-meter contour, from Cape Cod to Grand Manan, the frequency 
of occurrence (percentage of stations) has been about the same for one season as 
for another, 51 and Pseudocalanus was taken with equal regularity (70 to 80 per cent 
of the stations) over the western half of the basin west of the longitude of Mount 
Desert Island (long. 68° 30' W.) in July-August as in October-January, February- 
March, April, or May-June (the copepods have been listed at 39 stations from 
that region) ; but while it was recognized at three of the four December-May stations 
over the shallows west and southwest of Nova Scotia, out to the 100-meter contour, 
it failed at two out of five summer-autumn stations there. It appears in the lists for 
only eight out of 17 July- August stations in the eastern half of the basin, east of 
longitude 68° 30' W. (including the Eastern and Northern Channels), where it was 
taken at every station for September, January, March, and April, and at four out 
of five May-June stations. 
On Georges Bank and over the shelf off Marthas Vineyard it likewise occurred 
in all the vertical hauls for the spring of 1920 but failed at four out of eight July- 
August stations in 1913 and 1914, though present at all three stations off Marthas 
Vineyard on October 21 and 22, 1915 (stations 10331 to 10333; table, p. 298). Our 
few hauls outside the continental edge abreast the gulf also point to a definite and 
similar seasonal cycle for Pseudocalanus, it being present at six out of seven of the 
December-May stations but at only two of the five for May-October. Thus, while 
Pseudocalanus is uniformly frequent throughout the year in the western half of the 
gulf, irrespective of depth, and along the northern coast, it occurs somewhat less 
frequently and regularly in the southeastern and eastern part during the two-month 
period, July-August, than at any other time of year. Apparently it follows the 
same seasonal cycle, but with a decidedly greater impoverishment in summer, on 
the offshore banks and in the more oceanic water outside the continental edge, 
though more tows are needed in this region before a final pronouncement can be 
made. 
It must be borne in mind that any planktonic animal may or may not be taken 
most frequently when most abundant (may even be most frequent when least 
numerous), the relationship between the two measures of occurrence depending on 
the uniformity of distribution. In the case of P. elongatus the data afforded by 
40 In contrast, compare the seasonal fluctuations in the regional distribution of such an immigrant species as Sagitta serrato- 
dentata (p. 320). 
51 Eighty-five per cent for December-May, 90 per cent for June-October; total number of hauls, 51 
