of the Fishery Board for Scotland. 
225 
The saltness of the water, then, being helpful, the nature of the bottom 
may hinder or assist operations. The bottom should be sufficiently hard 
to prevent the tiles when laid in the water being silted up and covered 
with mud. Arcachon and the Morbihan form a great contrast in this 
respect. While the bottom at Arcachon is composed of gravel, sand, and 
mud, and presents a comparatively firm stratum, in the indentations of the 
Morbihan the bottom is of very soft mud, that would rapidly bury the tiles 
if they were placed upon it. In the East Schelde the conditions of 
bottom are more akin to what is found at Arcachon, and consequently the 
arrangement of the collectors is much the same. 
Another condition which is essential to success is that the spot chosen 
for placing the collectors should be in a sheltered locality, and not 
exposed to the violence of the sea. At St. Brieuc the neglect of this 
condition caused a loss of oysters and collectors, and seemed almost to 
thwart the efforts which the French were making in the new enterprise 
of artificial cultivation. 
The particular place for placing the collectors, in order that they may 
be clothed with a sufficient amount of spat, is where there is a gentle current 
and eddies carrying the embryos which have been set free from the 
mantle chamber of the mother. The embryos are thus brought in 
contact with the collectors and rest on them. 
As to the time when the tiles should be placed in the water, that varies 
at different points, all agreeing, however, that not till the embryos have 
been liberated from the mother's shell should the tiles be placed in the 
water. The reason for this is obvious. If the tiles are deposited too 
soon, they become covered with dirt and overgrown with, seaweed, 
ascidians, and polypes, and so do not offer a good situation for the young 
oyster to settle upon. The date at which they should be placed in the 
sea depends on the temperature of the water. When the temperature of 
the water has risen to 18° C. (64° Fahr.) the tiles are deposited. At 
Arcachon the tiles are deposited in the water from the 12th or 15th of 
June, or, in a cold season, as late as the beginning of July. In Brittany 
the water is not so warm, and so the tiles are not placed till sometime 
later, between the 25th June and the middle of July. In Holland they 
are deposited in June or July, the time depending on the season. The 
temperature-index is one way (the handiest in fact) of ascertaining the 
stage of development of the embryos ; the other is to examine the female 
organs, carefully note their condition, and ascertain the time taken for 
the extruded egg to develop till it becomes a free swimming pelagic 
embryo. 
The arrangement of the tiles differs at different places, as do also the 
size and the shape of the tiles. They are like ordinary roofing tiles, 
concave on one side and convex on the other. The tiles used at Arcachon 
are longer than those I have seen elsewhere. They are 20 inches long, 
9 inches broad at the one end and 5 at the other. In Holland and in 
the Morbihan, while the tiles are slightly shorter, they are of equal breadth 
at either end. In placing them they are so arranged that currents 
and eddies are promoted between different tiles and different rows of tiles. 
At Wemeldinge in Holland the tiles are laid down near the shore, 
outside of the dyke of the polder — polder is the land reclaimed from the 
sea — and are placed parallel to and against each other, the tiles in the 
row being placed obliquely to the bottom on which they lie. At Arcachon 
in France the tiles are deposited in rows, with their concave surfaces 
towards the bottom, each row of tiles being transverse to the one 
immediately above and below it. While, in the cases of some, especially 
the marines who hold pares, the tiles are placed in this way on the 
V 
