THE BEHAVIOR OF A PARASITIC COPEPOD 49 



experiments was undertaken. The results have convinced me 

 of the fact that in ordinary daylight, especially in sunlight, the 

 free swimming copepods move about close to the surface waters. 

 In weak light, and in total darkness they sink passively to 

 deeper regions. 



The migrations of water dwelling organisms is a problem 

 that has been studied by a number of investigators. Giesbrecht 

 (1892), in his splendid report on the pelagic copepods of Naples, 

 states that Weismann (1877), was the first one to attribute the 

 upward and downward movement of pelagic organisms to the 

 responses of these animals to light of different intensities. How- 

 ever, the first investigators to determine this question experi- 

 mentally were Groom and Loeb (1891), who worked on the 

 nauplii of the barnacle B alarms per for at us. In the laboratory, 

 these investigators found that when the young were subjected 

 to light of strong intensity, they reacted negatively, whereas 

 in faint light, they were positive. These reactions were similar 

 to the behavior of the nauplii in the open sea, where the larvae 

 are found clinging to the surface of the water at night only, 

 while during the day they swim about in deeper regions. Based 

 on these observations, Groom and Loeb came to the following 

 conclusion : " Das starke Licht bei Tage treibt die Tiere in 

 die Tiefe, das schwache Licht, das auch in der Nacht vom Him- 

 mel ausgesandt wird, zwingt sie wieder in die Oberflache em- 

 porzusteigen." 



Loeb (1893) has brought forth additional evidence among 

 marine copepods as well as other animals, such as Limulus and 

 the Annelid Spirographis, which tends to strengthen the theory 

 that light causes the periodic migrations of pelagic organisms. 

 In this paper, however, Loeb calls attention to other factors 

 besides light, such as gravity, which may also play an import- 

 ant part in determining these periodic movements. 



Parker (1901), in his studies on the daily migrations of the 

 marine copepod Labidocera aestiva, found that light was the 

 most important factor in the vertical movements of these organ- 

 isms. "Labidocera aestiva frequents the surface of the sea from 

 sunset to sunrise. From sunrise to sunset, it is presumably in 

 deeper waters. Its migrations are explained as follows : Females 

 rise to the surface with the setting sun, because they are posi- 

 tively phototropic to faint light and negatively geotropic; they 



