AMPHIPOD GENUS PARATHEMISTO BOWMAN 355 



Part of the variation in numbers may be caused by seasonal changes 

 in the intensity of breeding. However, females with ova or embryos 

 in the brood pouch were abundant at all but the southernmost sta- 

 tions on all three cruises. Juveniles which had recently left the brood 

 pouch were also widespread, and it is apparent that breeding goes on 

 during most if not all of the year. 



Another possible explanation for the seasonal change in catch is 

 that the population inhabited deeper water in March and November 

 than in July. Some evidence for this is found in a comparison of day 

 and night hauls. In both March and November the mean number per 

 positive haul was much greater for the night hauls than for the day 

 hauls, nearly five times as great in March and more than three times 

 as great in November. These differences suggest that diurnal vertical 

 movements were occurring during these months, and that during the 

 day part of the population was below the level of the net hauls. In 

 July, however, there was almost no difference between the mean num- 

 ber per station for the day hauls and that for the night hauls. Here 

 diurnal vertical migrations were very limited or lacking, and probably 

 at least most of the populations were living at depths not greater than 

 70 meters. 



2. Northwestern Pacific: I have been able to examine a limited 

 number of plankton samples from the northwestern Pacific. In addi- 

 tion to Albatross samples, principally from the Sea of Japan, I have 

 studied specimens from Carnegie stations, material sent to me by 

 Motoda, Nakai, and Yang, and a few specimens from salmon stomachs 

 forwarded to me by William Aaron of the University of Washington. 



All the samples from the Japan and Okhotsk Seas contained P. 

 japonica. In addition P. japonica was found at Albatross stations 

 4805 (east of Iturup Island, Kuriles) and 4806 (east of Cape Yerimo, 

 Hokkaido), and in one of Motoda's samples from east of Cape Esan, 

 Hokkaido. In these latter three samples P. pacifica also occurred, 

 but in much smaller numbers than P. japonica. 



Further east only P. pacifica occurs. Detailed planktonic surveys 

 are needed to establish the eastern boundary of P. japonica. P. paci- 

 fica extends to Japanese coastal waters, but does not occur in the Japan 

 Sea and probably not in the Sea of Okhotsk, where it is replaced by the 

 larger P. japonica. 



In 1948 Irio reported on the distribution of a number of pelagic 

 amphipods in waters adjacent to Japan, including a species of Para- 

 themisto which was listed as "Parathemisto sp. A." In a later paper 

 (1957b) this species is illustrated under the name Themisto gracilipes 

 Norman, but the illustrations are clearly of Parathemisto japonica. 

 Probably both P. japonica and P. pacifica were present in Irie's col- 

 lections, and possibly P. gracilipes in the stations south of Japan. 



