70 NATURE AND LIFE. 



epidermis, etc. The shape of the different cells varies very 

 much in different species. Some of them even assume 

 very odd forms. The multipolar cells of the central nerve- 

 substance resemble polypi with singular arms. Others are 

 star-shaped, others spindle-formed, etc. The fibres have 

 the shape of a narrow ribbon, lengthened out and very 

 thin, sometimes inclosing one or several nuclei. The fun- 

 damental elements of the muscles are fibres of two kinds : 

 those of organic life, which are smooth, and varying in 

 length between six - hundredths of one - thousandth of a 

 millimetre and five-tenths of the same dimension; and 

 those of the animal life, which are striated and very much 

 smaller. The conjunctiva tissue and the elastic tissue are 

 also made up from special fibres. Those elements having 

 the shape of tubes are the perineura, which wraps the 

 primal elements of the nerve-tubes in the nerves of animal 

 life, and in the white filaments of the great sympathetic 

 nerve ; the myolemma, which surrounds the primal fibres 

 of the muscles of animal life ; the capillary vessels, the 

 tubes of the glands, and the parenchyma, and last the nerve- 

 tubes. These latter, which make up the larger part of the 

 nerves, have a diameter varying from one-hundredth of a 

 millimetre to one ten-thousandth of that dimension. Mir- 

 bel wrote, in 1835, that the cells or " utricles " are so many 

 living individuals, each enjoying the property of growing, 

 of multiplying, of certain limited modifications, working 

 in common for the building up of the plant of which they 

 become themselves constituent materials. He added, as 

 Turpin had already expressed it in 1818, that the plant is 

 thus a collective being. We can now say the same thing 

 of the animal. It too is a collective being, made up by 

 the agglomeration of the fibres, tubes, and cells, which we 

 have just described. We are only federations of anatomi- 

 cal elements. 



Until the time of Robin, the anatomical elements had 



