BIOLOGICAL STUDY OP CHESAPEAKE BAY WATERS 
337 
was a tendency for S. elegans to remain near the bottom, at least during the bright 
half of the day. As might be expected, we found S. elegans in water of 29 to 30 per mille 
salinity outside of the capes, but large numbers of small specimens grading up to speci- 
mens over 30 millimeters long were found in good condition at area Y in water of not 
more than 13 per mille salinity. (Surface salinity at this area, 5.26 per mille; 
bottom salinity, 18 meters, 12.99 per mille.) This haul was made in March, 1921; 
and undoubtedly it was not an unusual condition for that time of the year, because 
the log in which were recorded the conspicuous organisms in the hauls at the time they 
were brought to the surface shows that in March, 1920, and March, 1922, sagittas 
were present in the same region, close to area Y (surface) and at area X, respectively. 
The salinity of the water in which the specimens were found at the former area was 
11.63 per mille and at the latter area not more than 16.79 per mille. The great abun- 
dance of S. elegans in Chesapeake Bay even at the time of low salinities and the small 
numbers of S. serrotodentata, S. enflata and other sagittas, in so far as our records 
show, indicate that S. elegans is adapted to a large range of salinities, while the other 
species are not. However, it does not follow that the degree of salinity of the water 
is the only factor which accounts for the horizontal distribution found in Chesapeake 
Bay. The specimens caught at the surface were too meager in number to make any 
comparison of the relative numbers at the mouths of rivers as compared with other 
regions or to study differences on the east and west sides of the bay which might 
possibly be due to differences in salinity. 
It is generally believed that the temperature of the water is another factor 
governing the horizontal distribution of Sagitta elegans. The scarcity of specimens in 
the bay during the summer cruises, when the comparatively shallow waters are heated 
to as much as 24° C. at the bottom and 27° C. at the surface, and their abundance 
during the coldest season, when the temperature drops to near 0.0° C. at the surface 
and a degree or so higher at the bottom, suggests the importance of temperature in 
determing the distribution. But other factors, such as an abundance of food, must be 
be considered ; and in this connection it is of special interest to note that during the 
March-April cruise (1921), when S. elegans was so abundant in the upper bay, at 
least, C. B. Wilson found the copepod Acartia clausii in maximum numbers in the 
same region. It is known that copepods are an important food of sagittas, and 
Bigelow (1926, p. 320) has pointed out the probable dependence of the distribution 
of S. elegans on the calanoid copepod plankton. In the case of vertical distribution 
the intensity of light should not be neglected. Finally, dominating fall and winter 
in-going bottom currents must be considered as probable factors affecting the seasonal 
and horizontal distribution of S. elegans in Chesapeake Bay. 
Our records show that Sagitta enflata was scarce in Chesapeake Bay during all 
the cruises. It was taken almost as seldom as S. serratodentata. S. enflata is recog- 
nized as a tropical form, characteristic of the surface waters of the Gulf Stream (Hunts- 
man, 1919, pp. 425, 426; Ritter-Z&hony 1911, p. 17; Bigelow 1917, p. 298; Bigelow 
1926, p. 334). Huntsman has found it as far north as 43° 30' N, off Nova Scotia; 
while Bigelow has taken it off Marthas Vineyard, off the coast of New Jersey, and as 
far south as the region of Chesapeake Bay. Fish (1925) does not report it from Woods 
Hole.f|No specimens were captured in the Chesapeake Bay during our July and 
August cruises (1920), although a few were found outside; but on the October cruise 
4 specimens were taken at area Q, 2 at area A, and 10 at area B. The two latter areas 
are near the mouth of the bay while the former one is a little farther north abreast of 
