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In the third type, neither a single queen nor a single worker is able to carry on all of the biological tasks any more than a muscle-cell or an unformed egg of Hydra can maintain itself capably in isolation.
In this way we will have the gland-cell, the muscle-cell, and the nerve-cell, each cell destined to produce one of these organs developing others "after its kind," the result being that it is soon surrounded with numerous companions doing a similar work, making up in this way a particular tissue or organ gland, muscle, or nerve which in the aggregate has for its function the work of the particular cells composing it.
In like manner, in spite of the complicated apparatus which supplies oxygen and removes carbon dioxide, the respiratory system, respiration is finally the work of the cell, as in amoeba; a muscle-cell respires exactly as does the one-celled animal.
Of the muscle-cell, the liver-cell, and the one-celled animal we may affirm the same properties, but the difference is that while all are secretory the liver-cell is eminently so, and produces bile, which other cells do not; that while it is but feebly contractile, or susceptible of change of form, the muscle-cell is characterized by this property above all others.
In the first case, it provides the muscle-cell with a large reserve deposited in advance: the quantity of glycogen contained in the muscles is, indeed, enormous in comparison with what is found in the other tissues.
It has been already pointed out that respiration is in all animals, in the end, the same process. The one-celled animal and the muscle-cell respire in the same way, and with the same results oxidation, combustion, and resulting waste products.
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