SECT. 17.] CELL-NETWORKS. 29 



a. Horny Plates, flattened polygonal or fusiform Cells, the mem- 

 branes of which have blended with the contents; in the epider- 

 mis, the laminated pavement epithelia, the nails and hairs. 



b. Contractile Fibre-cells ; fusiform, slightly flattened, consider- 

 ably elongated cells, the membranes of which, together with their 

 pulpy contents, have become transformed into a contractile sub- 

 stance, in the smooth muscular fibres. 



c. Striated Muscular Fibres; long fibres with many nuclei, with 

 a distinct envelope, and a contractile, often fibrillated, interior 

 substance, originating from the excessive growth of single cells. 



d. Fibres of the Lens ; very elongated cells, with viscid, more 

 or less firm contents, rich in albumen. 



B.— HIGHER ELEMENTARY PARTS. 



§17. The higher elementary parts correspond genetically to an 

 entire sum of simple ones ; and, indeed, as far as we yet know, it 

 is only the cells which are capable of producing them. The man- 

 ner in which this happens is various. That is to say, the cells, 

 while they coalesce, either retain their cell-nature, and in part also 

 their independence; and then there arise, according as they are 

 fusiform or stellate cells, cell-fibres and cell-networks ; or the cells 

 entirely lose their independence on union; and, in this case, accord- 

 ing as the cells are arranged in linear series, or are wholly con- 

 nected with each other on all sides, form elongated, elementary 

 parts, networks and membranes, the two former of which again, 

 according to the kind of metamorphoses of the contents of the 

 united cells, may appear as fibres, bundles of fibrillar, tubes, fibrous 

 m f works, and as plexuses of tubes. As these elementary parts will 

 he spoken of more in detail below, in treating of the tissues, a 

 short enumeration of them here may suffice. 



They are : 1. Higher Elementary Parts, which present, more or 

 less distinctly, the Cells composing them. 



1. Cell-networks from the tissue of connective substances. To 

 this category belong the corpuscles of connective tissue ( Virchoio), 

 the cartilage-cells of certain plagiostomatous fish (Leydig), all anas- 

 tomosing pigment-cells, the lacunas of bone and the dental tubes, 

 the cells of the fat-body of the Lepidoptera (H. Meyer, Zeitschr. 

 f iv. Zool.i. p. 178). 



2. Cell-networks of Muscular Tissue. Anastomosing, smooth, 

 or transversely striped cells of the heart and skin of the lower 

 animals. 



3. Cell-netivorks from Nervous Tissue. Anastomosing nerve- 

 cells of the retina and of the central organs. 



