36 University of California Puhlications in Zoology [Vol. 13 



We obtained 73 specimens of Euplokamis in 13 hauls for which 

 temperatures were taken and 65 of them appeared when the tempera- 

 ture ranged from 18 ?1 to 19°. The frequencies are so much higher 

 then, also, that it hardly seems that the results are due to coin- 

 cidence. 



The results with regard to salinity are decisive as far as they go, 

 but since there are only seven successful hauls the mere mention of 

 the results is sufficient. Thirty-five animals were obtained, of which 

 32 were taken in water ranging from 33.61 to 33.65 in salinity, two 

 at 33.60 or less and one between 33.60 and 33.70. 



Four specimens of Euplokamis were obtained in four hauls with 

 the Nansen nets, and all between 30 and 75 fathoms. There was one 

 specimen in a haul with the Kofoid net at 150 fathoms. 



Beroe is represented by sixty-six specimens taken in four hauls. 

 Sixty-two of these animals were present in two June hauls made be- 

 tween 6 and 8 p.m. The temperature during one of the hauls, which 

 obtained three animals, was 16?3 ; the temperature of the other haul 

 is unrecorded, but there is reason to think it was about 16°. Here 

 also is the indication of specific behavior when these results are com- 

 pared with those relating to the other ctenophores. Beroe was ob- 

 tained in one haul with the Nansen net, there being nine specimens 

 from a depth of 12 fathoms ; the net was hauled horizontally. 



SUMMARY 



If the behavior of the ctenophore Pleurohrachia Ijachei is com- 

 pared with that of the chaetognath Sagitta hipundata (Michael, 

 1911) or of the copepod Calanus flnniarcMcus (Esterly, 1912), the 

 most striking difference is in the exceeding rarity of the ctenophore 

 in sub-surface hauls. The chaetognath named and the copepods in 

 general appear to have well-defined levels below the surface (centers 

 of migration) at which they are more abundant than at the surface, 

 at certain times, and from which they move to or tow^ard the surface 

 at regular intervals during the twenty-four hours. There is no evi- 

 dence at hand that the ctenophores perform these depth migrations, 

 though they are absent from the surface at certain times of the day. 

 It is impossible to say what becomes of the animals during the time 

 they are absent from the surface. It is hardly probable that their 

 absence from the surface at specified times is due to coincidence. 



