10 REPORT— 1879. 



crayfish the cells of the embryo throw out pseudopodia by which, exactly 

 as in an Amceba, the yolk- spheres which serve as nutriment for the 

 embryo are surrounded and engulphed in the protoplasm of the cells. 



I had shown some years ago 7 that in Myriothela pseudopodial pro- 

 cesses are being constantly projected from the walls of the alimentary 

 canal into its cavity. They appear as direct extensions of a layer of 

 clear, soft homogeneous protoplasm which lies over the surface of the 

 naked cells lining the cavity, and which I now regard as the ' Haut- 

 schicht ' or cortical layer of these cells. I then suggested that the func- 

 tion of these pseudopodia lay in seizing, in the manner of an amceba, 

 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, 8 who has seen 

 the cells which line the alimentary canal in these animals act like inde- 

 pendent Amoeba?, and engulph in their protoplasm such solid nutriment 

 as may be contained in the canal. When the Planaria was fed with 

 colouring matter these amoeboid cells became gorged with the coloured 

 particles just as would have happened in an amceba when similax*ly 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 scat- 

 tered constituents of the tissues as the pigment cells, or in cells des- 

 tined 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 less real. With 

 this autonomy of each element there is at the same time a subordination 

 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 physiolo- 

 gical division of labour. In the lowest organisms, where the whole being 

 consists of a single cell, the performance of all the processes which con- 

 stitute its life must devolve on the protoplasm of this one cell ; but as 

 we pass to more highly organised beings, the work becomes distributed 

 among a multitude of workers. These workers are the cells which now 

 make up the complex organism. The distribution of labour, 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 pro- 

 cesses, which are accumulated in the single cell of the unicellular or- 

 ganism become in the more complex organism differentiated, some being 

 intensified and otherwise modified and allocated to special cells, or to 



' Loc. cit. 



8 Ueber die Verdaxmngsorgane einiger Suss /raster- Tiwbellarien. Zoologisehcr 

 Anzeiger, December 1878. 



