210 THE PRESENT EVOLUTION OF MAN — PHYSICAL 



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 remem- 

 bering, 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 multicellu- 

 lar organism is a being compounded of unicellular 

 organisms, the cell-descendants, generally speaking, of a 

 pair of conjugated unicellular organisms, which cell- 

 descendants during the ontogeny, unlike the cell- 

 descendants 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 differ- 

 entiation 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 scaveng- 

 ing functions are capable of independent movements, 

 and are known as white blood corpuscles when occumng 

 in the blood, and as wandering connective tissue cells when 

 found in the tissues, the two designations probably signify- 

 ing 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 



