340 
PACIFIC SCIENCE, VoL IX, July, 1955 
TABLE 2 
The Number of Tetraplatia volitans Taken in a Vertical Series of Horizontal Closing-Net Tows 
June 12 and 13, 1952 
NIGHT SERIES 
DAYLIGHT SERIES 
Wire Out 
(Meters) 
Time 
Number of Specimens 
Wire Out 
(Meters) 
Time 
Number of Specimens 
10 
2152 
0 
Surface 
0913 
0 
4 
2219 
0 
10 
0935 
0 
25 
2253 
0 
25 
0955 
0 
40 
2400 
0 
40 
1030 
0 
60 
0029 
1 
80 
1130 
0 
100 
0135 
1 
100 
1155 
0 
150 
0205 
1 
150 
1223 
0 
200 
0243 
1 
200 
1300 
0 
300 
0325 
1 
300* 
1340 
0 
400 
0410 
4 
300 
1420 
0 
400 
1455 
16 
* Net did not close. 
form which undergoes a diurnal vertical mi- 
gration, approaching the surface at night and 
returning with the advent of sunrise to rather 
great depths. It should be pointed out that 
most of the samples of Tetraplatia which have 
been obtained were collected at positions 
where the depth to the bottom was greater 
than 1,000 meters and in many cases in water 
several thousand meters deep. 
The sample mentioned above containing 
16 specimens was one of a group of horizontal 
tows taken in a vertical series on June 12 and 
13, 1952 at 33° 28.5' N. by 117° 46.7' W. 
Tetraplatia volitans was taken in seven of the 
21 tows of this series (six tows of the night 
series and one of the day series). The results 
from this series of samples are shown in 
Table 2. 
It will be noticed in this vertical series that 
by no means all of the specimens were taken 
near the surface at night, but instead they 
seem to be fairly evenly distributed over 
depths of about 40 to 300 meters (assuming 
a wire angle on these tows of about 45°). In 
the vertical series reported earlier in this study 
the center of the population, at night, seemed 
to have been in the neighborhood of 40 
meters. It therefore is apparent that although 
some tetraplatians undergo a marked vertical 
migration this is not necessarily the case, 
although these animals, almost without ex- 
ception, descend to or stay at depths of 250 
meters or more in the daytime. 
Little information is available concerning 
the depths to which Tetraplatia may descend. 
Specimens have been recovered from samples 
in which the net fished from about 1,000 
meters to the surface in the Pacific, while 
some of the "Meteor” specimens were taken 
in net hauls to depths of 900 meters and the 
"Valdivia” specimens to depths as great as 
2,500 meters. However, since these net hauls 
were not closing-net tows, little but specula- 
tive results can be gleaned from them and no 
exact information is available concerning the 
lower limits of the vertical distribution of 
Tetraplatia . The 44 specimens from Monterey 
Bay add a little information along this line 
since it appears from the 11 tows which cap- 
tured Tetraplatia that in general the deeper 
the tow the more specimens were captured. 
These tows were continuous from the depth 
