PLANKTON OF THE GULF OF MAINE 353 



hydroid stage — and consequently that the medusa is independent of the coast line and 

 of the bottom at all stages in development. Its distribution is therefore wholly 

 independent of distance from land or from shoal water. 



Aglantha, like many other medusas, was first recorded from the Gulf of Maine by 

 Alexander Agassiz (1865), who detected both large, sexually mature medusas and 

 young ones at Nahant, Mass., during the summers of 1S63 and 1864, since when 

 it has been reported both by Hargitt (1905) and by Mayer (1910) as common in 

 spring off the shores of southern New England. Consequently it was no surprise to 

 find it in our plankton hauls at many stations in the Gulf of Maine. The localities of 

 capture, as appears on the chart (fig. 99), are concentrated in a peripheral zone 40 to 

 60 miles broad, paralleling the coast from Cape Cod to Cape Sable and spreading 

 thence southward and westward across Browns Bank, the Eastern Channel, and 

 following the southern half of Georges Bank westward; but we have never taken 

 a single specimen of Aglantha in the central waters of the Gulf or over the northern 

 part of Georges Bank. 



The reader need but compare the chart of Aglantha with the corresponding chart 

 for Beroe (fig. 102) or for Pseudocalanus elongatus (fig. 83), animals equally pelagic at 

 all stages and of similar temperature affinity but regularly and constantly endemic in 

 the Gulf of Maine, to note the sharp contrast between the definite localization of 

 the records for Aglantha 93 and the universality of the others. 



Although we have never found Aglantha with sufficient regularity (and seldom in 

 sufficient abundance) to regard it as a characteristic member of the plankton of the 

 gulf, it has occurred often enough and at stations indifferently enough spaced to show 

 that it may be expected anywhere and at any season in the area inclosed by the 

 curve on the chart. Within this area the locality records show no definite concen- 

 tration in one side of the gulf or the other, nor do they correspond to the depth of 

 water, and our experience has been that the local presence or absence of Aglantha 

 in the gulf at any particular time is as independent of precise temperature or salinity 

 as it is of depth, the close neighborhood of land, or the contour of the bottom. Its 

 distribution closely mirrors the anticlockwise circidation of the upper strata of 

 water in the gulf. The natural inference from this is that the continued presence of 

 Aglantha within the gulf depends more on immigration from the east and north than 

 on local reproduction. Once such immigrants have passed Cape Sable they follow 

 right around the gulf, first north then west, southwest, and south in their involuntary 

 journey, with little more tendency to spread toward the center of this great eddy 

 than have the various fish eggs or other animals of neritic nature that are set free 

 near the coast lino. In this its distribution in the gulf parallels (though it does not 

 exactly reproduce) that of the chaetognath Eukrohnia hamata, another common visi- 

 tor from colder seas to the east and north, which occurs far more regularly around 

 the periphery of the deep basin than in its center and spreads southward along the 

 slope of Georges Bank but at a deeper level than Aglantha. 



« For locality records of Aglantha for the years 1913 to 1916, see Bigelow, 1915, p. 316; 1917, pp. 303 and 304; 1922, pp. 134 and 136. 

 During thespring of 1920 it was taken at stations 20044, 20046, 20049, 20055, 20056, 20058, 20054, 20067, 20068, 20071, 20072, 20073, 20074, 

 20075, 20076, 20077, 20079, 20081, 20087, 20096, 20105, 20107, 20111, 20115, 20116, 20118, 20122, 20128 ,and 20129, and at Stations 10490. 10491 

 and 10499 during December-January, 1920-1921. 



