26 
spat were on September 24th on an average !/, inch in length (see Table II No. 
14). I can remember distinctly, and have remarked upon it, that I was surprised 
to find the spat much smaller on the natural banks than on the collectors and 
artificial objects; but this seems to he the rule. In 1905 and 1906, when I was 
again investigating the spat at Volstrup in the Lim Fjord in August (see Table 
II No. 4 and 5), I found them to be only ca. Imm. or less. On August 1895 
the spat on the collectors had already reached up to !/, an inch in diameter (see 
Table II No. 13). 
At Volstrup which was investigated very carefully in 1905 and 06 it was 
found that many more oysters of the 0-group occurred in the shallow water (3—6 
feet), where we pole-dredged tor the oysters, than in deeper water of 12—18 feet 
where we dredged. A glance at Table III will further show that the »one-year 
old« oysters were also more abundant in the shallow than in the deeper water. 
In 1895, as mentioned, the spat were found fixed to various artificial 
objects, thus: on limed tiles, on spars of fir, on a wooden barrel hung overboard 
at the Biological Station, on pieces of granite hanging in and on the barrel, on 
the bottom of the boat, on the wooden piles of the harbour. The barrel, in which 
there was no bottom, was used to provide the aquaria on board with air; it had 
a small hole at the top, from which a piece of guttapercha tubing carried the air 
pressed out by the weight of the stones into the aquaria; when the barrel filled 
with water (2 times in the day), it was hoisted up a moment and new air allowed 
to enter below, whilst the water ran out. On August 3rd the oyster spat was 
observed both on the barrel itself and on the stones hanging outside and inside. 
Quantities of other organisms were also found here, e.g. Ciona canina, Phallusia 
sp., Pomatoceros, Balanus, diatoms and algæ; but it was obvious that the plants 
dominated on the sunny side of the barrel and stones; the green algæ were only 
situated on the upper parts; on the other hand the animals kept more to the 
shaded sides; and inside the barrel where there must have been extremely little 
light (only from below), many Phallusia were still fonnd and a few oysters but no 
plants. There is no doubt that light plays a great part during the fixing of the 
oyster spat; but whether the reason is that the plants quickly fix themselves on 
the light side and thus hinder any later fixing of the oysters, I must leave undecided. 
We may compare with this the experiments made at Roscoff by Lacaze-Duthiers 
during a number of years to get the oysters to spawn in a closed basin. The 
experiment seems to have been successful beyond all expectation (Archives de 
Zoologie experimental (3) T. 1. 18941). My experiments with collectors have only 
been made on a very small scale; the material which gave the hest result was 
tiles coated with lime, which seems to be the only method now usually employed 
im France and Holland. In Thisted Harbour in the autumn of 1895 I observed 
5 pleasure yachts, which had lain the best part of the summer in the harbour; 3 
had been tarred in the spring, and the other two coated with a patent paint; on 
July l1st they were all cleaned and again put out, and perhaps most of the patent 
paint had thus been cleaned off. The bottom of these boats was much covered 
with various animals and plants, but some almost exclusively with oyster spat. 
N. et revue pg. XXV. 
