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 

