much controverted question of the transmission of acquired traits in very high and very low organisms, we may, with profit, pause to consider it, always remembering, however, that the main tenor of our argument is not affected by this side issue, decide it how we may.
If we hold, as I think we must, that the multicellular organism is a being compounded of unicellular organisms, the cell-descendants, generally speaking, of a pair of conjugated unicellular organisms, which celldescendants during the ontogeny, unlike the celldescendants of a pair of conjugated infusorians, remain adherent and undergo morphological and physiological differentiation along definite lines of descent, we may well believe that along certain of these lines the differentiation is such, that the cells belonging to them become functionally adapted to resist and repair any injuries which may befall the organism, whether at the surface or in the interior, whether in the solid tissues or in the fluids such as the blood which nourish and cleanse those tissues. Marvellous as such a functional adaption may appear at first sight, it does in fact occur, and is, after all, less marvellous than the adaption to various other functions of certain other kinds of cells, as, for example, skin, gland, muscle, and nerve-cells which have departed farther from the ancestral amoeboid type.
The cells which perform the reparative and scavenging functions are capable of independent movements, and are known as white blood corpuscles when occurring in the blood, and as wandering connective tissue cells when found in the tissues, the two designations probably signifying identical things in different situations, for the white blood corpuscles apparently differ in no respect—neither morphologically nor physiologically—from the wandering connective tissue cells, and have been seen migrating
