As it is a staple food with the poorer classes, the deficiency is made up through importation.
This deficiency is made up by the addition of auxiliaries or suffixes.
Jacobsen on some occasions found water in the surface layers of the Baltic supersaturated with oxygen, which he ascribed to the action of the chlorophyll in vegetable plankton; in other cases when examining the nearly stagnant water from deep basins he found a deficiency of oxygen due no doubt to the withdrawal of oxygen from solution, by the respiration of the animals and by the oxidation of the deposits on the bottom.
This deficiency is very usual in the class; at the same time, many Lamellibranchs have tentacles on the edge of the mantle supplied by a pair of large well-developed nerves, which are given off from the cerebro-pleural ganglion-pair, A, When free swimming, shows the two dentigerous valves widely open.
There is, however, a yearly deficiency of more than £6000.