STRUCTURE. 189 



sue), muscular tissue, nervous tissue. These severally con- 

 tain sub-kinds, each of which is a complex of differentiated 

 cells. Being brief, and therefore fitted for the present pur- 

 poses, the sub-classification given by Prof. R. Hertwig may 

 here be quoted ; — 



*'The physiological character of epithelia is given in the fact that 

 they cover the surfaces of the body, their morphological character in 

 that they consist of closely compressed cells united only by a cement- 

 ing substance. 



"According to their further functional character epithelia are 

 divided into glandular epithelia (unicellular and multicellular glands), 

 sensory, germinal, and pavement epithelia. 



" According to the structure are distinguished one-layered (cubical, 

 cylindrical, pavement epithelia) and many-layered epithelia, ciliated 

 and flagellated epithelia, epithelia with or without cuticle. 



' ' The physiological character of the connective tissues rests upon 

 the fact that they fill up spaces between other tissues in the interior 

 of the body. 



'■ ' The morphological character depends upon the presence of the 

 intercellular substance. 



"According to the quantity and the structure of the intercellular 

 substance the connective substances are divided into (1) cellular (with 

 little intercellular substance); (2) homogeneous; (3) fibrillar connec- 

 tive tissue ; (4) cartilage ; (5) bone. 



"The physiological character of muscular tissue is contained in 

 the increased capacity for contraction. 



''The morphological character is found in the fact that the cells 

 have secreted muscle-substance. 



" According to the nature of the muscle-substance are distinguished 

 smooth and cross-striated muscle-fibres. 



"According to the character and derivation of the cells (muscle- 

 corpuscles) the musculature is divided into epithelial (epithelial mus- 

 cle-cells, primary bundles) and connective-tissue muscle cells (con- 

 tractile fibre-cells). 



"The physiological character of nervous tissue rests upon the 

 transmission of sensory stimuli and voluntary impulses, and upon the 

 co-ordination of these into unified psychic activity. 



"The conduction takes place by means of nerve-fibres (non- 

 medullated and medullated fibrils and bundles of fibrils); the co- 

 ordination of stimuli by means of ganglion-cells (bipolar, multipolar 

 ganglion-cells)." ( General Principles of Zoology^ pp. 1 17-8.) 



