DIVISIONS OF ZOOLOGY. 9. 
in a tough intercellular matrix. Bone is a form of connec- 
tive tissue in which the matrix is impregnated with lime 
carbonate, and phosphate. pitheliwm is the outer layer of 
cells, having more or less thick walls, on any free surface of the 
body, whether that surface be external or internal; when the 
cells are furnished with cilia, it is called ciliated epithelium. 
Glandular tissue is a modification of epithelium, always 
consisting of cells which secrete various substances; they 
either retain their original position between the other cells 
of the layer, or they sink beneath the level of the epithelium, 
and open between the other cells by a fine duct formed by 
the membrane of the cell; they thus form ylands. (2) Mus- 
cular tissue is composed of contractile fibres. It is of two 
kinds, striped and unstriped. Striped muscular tissue 
consists of very long fibres made up of a delicate sheath, or 
surcolemma, enclosing a substance which is closely striated 
transversely ; unstriped muscular tissue is composed of 
elongate or fusiform fibres without any cell wall, and not 
showing any transverse striz, but each containing an elon- 
gated nucleus. (3) Nervous tissue. Nerve fibres are generally 
formed by a medullary sheath surrounding a finely granu- 
lated viscid substance; in some, however, the medullary 
sheath is wanting. Verve cells consist of a nucleated mass 
of granulated protoplasm without any cell wall. These 
cells generally send out long processes, called poles; they 
occur principally in the ganglia. 
Paleontology is a branch of Morphology exclusively 
confined to the study of extinct animals. Taxonomy, or 
classification, is a concise statement of the results of Mor- 
phology. 
Physiology is the study of the functions, or uses, of 
organs. It is essentially experimental in its method, but. 
partly observational as well. The functions of animals are 
