294 bulletin: museum of comparative zoology. 



and the fact that the richness of these decreased, while that of the 

 nearby stations increased, is good evidence that copepods were actu- 

 ally dispersed from them throughout the neighboring waters. 



The May swarm off Cape Ann (Station 10266) consisted chiefly 

 of very young stages of Calanus, with occasional older stages, and of 

 Pseudocalanus; i. e., it was an actual growth center, not an evidence of 

 immigration, and this agrees with our earlier observations that cope- 

 pod nauplii appear in swarms in Gloucester Harbor in early May fol- 

 lowed by great numbers of young Calanus in the adjacent w^aters later 

 in the month (1914b, p. 407). The May swarm in the Eastern Basin 

 (Station 10270) contained a much larger proportion of adult Calanus 

 fimnarchicus, with comparatively few very early stages; hence, so far 

 as internal evidence goes, it might either have represented an immigra- 

 tion, or a late stage in a local reproductive cycle, the unmistakable 

 influence of the Cabot Current in this region (p. 224) giving the first 

 of these alternatives an a j^nori probability'. But as there are no 

 records from the waters further south or east in May, and it is not 

 known whether copepods dwindle almost to the vanishing point in 

 the eastern half of the Gulf in early spring as they do in the western, 

 indeed nothing is known of the plankton there from September to 

 May, and the question remains open. 



Sagittae. — Sagittae were taken at nearly all stations, both in 1914 

 and in 1915; but the quantitative importance of this group, in the 

 plankton as a whole, differed greatly in different regions. Thus in 

 July 1914, Sagittae swarmed on the northeastern edge of Georges 

 Bank (Station 10224, Fig. 79) and again in the Northern Channel 

 (Station 10229), where the meter-net, at 100 meters, yielded upwards 

 of three liters. The opposite extreme was found on Brown's Bank 

 (Station 10228), off Shelburne (Station 10231), off Halifax (Station 

 10237), and off Penobscot Bay (Station 10250), where the catches were 

 respectively, two, seven, five, and two specimens; while none were 

 taken in the basin north of Le Have Bank (Station 10235). In 1915 

 Sagittae formed a considerable portion of the catch off Lurcher Shoal 

 in May (Station 10272) and near Shelburne (Stations 10291, 10295) 

 in June; while they swarmed in Massachusetts Bay late in Septem- 

 ber (Station 10321) and off Marthas* Vineyard in October (Station 

 10232). But nowhere in that year were they as abundant as the 

 local swarms of the preceding season. 



Our experience has been that Sagitta elcgans and S. serratodentata ^ 



1 Identifications follow Ritter-Zahony 1911 and Michael, 1911. 



