ELEMENTARY FORMS. 23 



elongated and pointed (e. g., in the granular pigment, in the blood, 

 in the muscular tunic of the intestines). Others attain a size of 

 more importance (fat cells), or diminish in size (the lymph glob- 

 ules, if they become changed into blood corpuscles) ; they lose 

 after a time their nucleus (the mature blood corpuscles) ; their 

 parietes become thickened (cartilage cells). 



17. In most tissues the cells blend together and coalesce. We 

 find remaining, 



1. The cavities of the cells unaltered, as their thickened walls blended 

 together (in true cartilage, and osseous tissue), or the parietes impinging upon 

 one another are broken through, so that continuous tubes arise (renal and 

 seminal tubuli, perhaps also capillaries) ; or, 



2. The cavities disappearing, their parietes lying flat together, so that the 

 cells form solid laminae, which appear to be spread out either in a mem- 

 branous or fibrous form, according to the position. 



Here belongs also the coalescing of complex (endogenous) cells [see 

 before], which are transformed into the primitive fibres of the nerves, arid 

 the primitive bundles of the animal muscular tissue. 



3. The nuclei of the cells elongate, coalesce, and thus form the " nucleus 

 fibres," which, much stronger than the cell fibres, upon which they are found, 

 are distinguished from them, also, by their insolubility in acetic acid. They 

 are either rectilinear, spiral, or like a tendril, according to the position of the 

 nucleus in the cell. 



18. As the cells are dislodged from their situation, or become 

 again formed into the homogeneous mass of cytoblastema out of 

 which they arose, intervals are formed which are filled with fluids 

 or air ; these are the intercellular passages. They are circum- 

 scribed by layers of cells, and appear, after the metamorphosis of 

 the cells into fibres, as canals and cavities (closed and open vascu- 

 lar cavities, lined with mucous membrane), with membranous or 

 fleshy parietes. It is, moreover, a matter of indifference whether 

 the structureless matter which also serves as a uniting medium be 

 solid, as in the bones, or fluid, as in the blood. The conditions 

 for the formation of proper tissues are given with the metamor- 

 phoses of the cells and nuclei; in a system of Histologia these 

 must also be received as a basis, and not that, more or less com- 

 posed of organs, as in the earlier systems. As however the 

 number of facts is yet too small for the complete carrying out of 

 a scientific arrangement, we must for the present observe a greater 

 number of casual successions. In this point of view, therefore, 

 anatomy can lay no claim to the name of a science. 



b. Individual tissues. 



19. External membrane, Epithelium. 



The non-vascular and nerveless thin investment which covers 



