+ 
Vol. 1X, Nos. 8-9.] Biological Work of the ‘‘ Investigator.’ 361 
[N.S.] 
ment, a richer fauna being brought down the coast by the tide, 
which in this region sets up and down the coast, the direc- 
tion of the flood being in the main to the N.-N.-W. and of the 
ebb to the S.-S.-E., or secondly, it might be due toa gon 
movement, the Copepoda sinking below the surface at the tim 
of the flood and high water, and rising again when the ebb tide 
is established. 
That it is not due to the former is shown by the fact that 
(1) the alteration in numbers does not exactly coincide with 
hours before high-water, and (2) although numerous tow-n 
tings were taken all over the region between the Middle Scdoel 
Islands and Byikhwaaw Bay, “there was no evidence of any 
variation in the local richness of the fauna such as this view 
presupposes to exist. We therefore have to fall back on the 
second explanation, and such evidence as | have te able to 
accumulate tends to show that this is the correct on 
A series of vertical hauls of the tow-net taken a different 
states of the tide in or near Byikhwaaw Bay, gave the following 
vertical distribution. 
No. or CoPEPODA OB- | 
TAINED. 
Posirion. | | 
Se ee | 
| State of Tide. 
N Ist 2nd 3rd 
: soe fathom. | fathom. | fathom. | 
| 
| 2,040| 2,550| .. | Adulte. 
se a ac “] 4,080 11,730 .. — Nauplil. 
| - 1,750 | 3,890 1,260 | Adults. 
esd ea es -) 2770 1,210, 3,850 Nauplil. 
3,560 | 1,790 1,630 Adults. 
16,290 | 1,020 3,310 Nauplii. 
Bie Te 1,660 | 2,550} 1,910 | Adults. 
High water ; 
5,090 12,200 11,200 Nauplii. 
he cause of this vertical movement I am inclined to 
attribute to a change in the density of the sea-water. T - 
such a change does actually cause a rise and fall of these animals 
has been shown by Professor Loeb. (1893, p. 96). 2 
Observations on the density of the aawhise were taken 
every morning at 7.30: the readings recorded were the mean 
