PROTOPLASM AND LIFE. 729 



" Hautschicht," or cortical layer, of these cells. I then suggested that 

 the function of these pseudopodia lay in seizing, in the manner of an 

 Amoeba, such alimentary matter as may be found in the contents of the 

 canal, and applying it to the nutrition of the hydroid. 



What I had thus suggested with regard to Myriothela has been 

 since proved in certain planarian worms by Metschnikoff,* who has 

 seen the cells which line the alimentary canal in these animals act like 

 independent Amoebae,, and ingulf in their protoplasm such solid nutri- 

 ment as may be contained in the canal. When the planaria was fed 

 with coloring matter these amoeboid cells became gorged with the 

 colored particles just as would have happened in an Amoeba when 

 similarly fed. 



But it is not alone in such loosely aggregated cells as those of the 

 blood, or in the amoeboid cells of the alimentary canal, or in such 

 scattered constituents of the tissues as the pigment-cells, or in cells 

 destined for an ultimate state of freedom, as the egg, that there exists 

 an independence. The whole complex organism is a society of cells, 

 in which every individual cell possesses an independence, an autonomy, 

 not at once so obvious as in the blood-cells, but not the least real. 

 With this autonomy of each element there is at the same time a sub- 

 ordination of each to the whole, thus establishing a unity in the entire 

 organism, and a concert and harmony between all the phenomena of 

 its life. 



In this society of cells each has its own work to perform, and the 

 life of the organism is made up of the lives of its component cells. 

 Here it is that we find most distinctly expressed the great law of the 

 physiological division of labor. In the lowest organisms, where the 

 whole being consists of a single cell, the performance of all the pro- 

 cesses which constitute its life must devolve on the protoplasm of this 

 one cell ; but as we pass to more highly organized beings, the work 

 becomes distributed among a multitude of workers. These workers 

 are the cells which now make up the complex organism. The dis- 

 tribution of labor, however, is not a uniform one, and we are not to 

 suppose that the work performed by each cell is but a repetition of 

 that of every other. For the life-processes, which are accumulated in 

 the single cell of the unicellular organism become in the more complex 

 organism differentiated, some being intensified and otherwise modified 

 and allocated to special cells, or to special groups of cells, which we 

 call organs, and whose proper duty is now to take charge of the spe- 

 cial processes which have been assigned to them. In all this we have 

 a true division of labor a division of labor, however, by no means 

 absolute ; for the processes which are essential to the life of the cell 

 must still continue common to all the cells of the organism. No cell, 

 however great may be the differentiation of function in the organism, 



* " Ueber die Verdauungsorgane einiger Siisswasser-Turbellarien," " Zoologischer 

 Anzeiger," December, 1878. 



