Bathymetric Distribution — AlvarinO 
483 
Halicreas papillosum 30 mm in diameter were 
present at 775-685 m, and those 50 mm in 
diameter at 1242-1090 m. Specimens of Peri- 
pbylla hyacinthina up to 25 mm high appeared 
at 300-235 m, whereas at 840-690 m they 
were 35 mm high. Colobonema sericeum up to 
40 mm in height were found at 460-410 m, 
and below this level those 50 mm in height. 
CTENOPHORAE 
Beroe spp. extended in the night series from 
10 m (uppermost sampling) to 500 m, and 
during daylight from 0 to 525 m. 
CONCLUSIONS ON BATHYMETRIC DISTRIBUTION 
Several striking features were observed in 
the bathymetric distribution : 
1. The number of species of Chaetognatha 
and Siphonophorae in the upper 100 m was 
higher during daylight than at night. 
2. The number of specimens for the species 
of Chaetognatha present both in daylight and 
at night in the upper 100 m was either of the 
same numerical magnitude or, in most cases, 
higher at night. 
3. In general, the difference in the number 
of specimens observed in the right and left net 
for the upper 100 m was greater during day- 
light than at night. 
Points 1 and 3 suggest either that during 
daylight the patches of specimens are denser, 
or that at night the individuals are scattered 
throughout a bigger region, thus providing 
fewer individuals per cubic unit of water. This 
conclusion appears to be in contradiction with 
established statements, which maintain that 
planktonic organisms congregate more at night 
than in daylight. Another possibility is that they 
can avoid the net better in daylight than at 
night. The sky condition at night, when the 
hauls were taken, was one of darkness, with- 
out moonlight; but there are no data on bio- 
luminiscence. 
Therefore, these preliminary studies appear 
to indicate that individuals are not evenly dis- 
tributed, but that there is a small pattern of 
patchiness included in the total region popu- 
lated by certain species. By using the paired 
net it will be possible to detect either this 
patchiness within the distributional region of 
the species, or the flocking of individuals when 
disturbed (a general behavior response observed 
in nature). 
DISTRIBUTION OF THE ORGANISMS AND THE 
POSITION OF THE SCATTERING LAYER 
Unfortunately, samplings were not made at 
depths at which the scattering records appeared. 
However, they could be determined easily by 
correlating records and samples taken at the 
same time and date. For example, at 1238- 
TABLE i 
Species in the Upper no m Correlated with the Shallower Scattering (Daylight) 
CONCENTRATION OF INDIVIDUALS PER 10,000 M 3 OF WATER FILTERED 
group 
GREATER 
THAN 5,000 
4999-500 
499-50 
LESS THAN 50 
Chaetognatha 
S. bier it 
S. minima 
S. pseudoserratodentaia 
K. subtilis 
S. bipunctata 
S. dec ip 'tens 
S. enflata 
S. euneritica 
P. draco 
S. hexaptera 
S. pacifica 
S. scrippsae 
Siphonophorae 
M. atlantica 
E. russelli 
Ch. appendiculata 
N. reticulata 
E. spiralis 
L. subtiloides 
A. acaule 
St. bijuga 
Medusae 
L. tetraphylla 
P. discoidum 
C. alba 
Ctenophorae 
Beroe spp. 
