VARIOUS KINDS OF CELLS: TISSUES 23 



and function. Nevertheless all these various sizes and shapes 

 can be classified under a few leading forms, and a knowledge 

 of these forms is a necessary prerequisite for the understand- 

 ing of the language in which the bodies of the various kinds 

 of animals are described. Indeed these forms may be com- 

 pared to the alphabet of a language in which the various 

 kinds of animals are sentences of different kinds. It is the 

 necessity of learning alphabets of this kind which makes the 

 study of zoology and of other sciences appear so dull and 

 technical to the beginner. Once the alphabet has been thor- 

 oughly assimilated, zoology becomes intensely interesting. The 

 schoolboy struggling with his declensions and his vocabulary 



FIG. 3. Diagrammatic representation of simple 

 columnar epithelium containing gland cells and 

 sense cells ; cut, cuticle ; gl, gland cell ; n, 

 nuclei ; s, sense cell. 



finds learning Latin dull work, but the finished classical 

 scholar finds the reading of the ancient authors stimulating, 

 elevating, and fascinating. 



The simplest kind of cell is a columnar one with outer 

 and inner terminal faces, and with a varying number of sides 

 which fit against the sides of similar cells, so that the whole 

 together constitutes a pavement, or as it is termed in zoology 

 an epithelium (Gr. epi, upon ; thelion, a tile). Such " pave- 

 ments " form the external covering of the body in very many 

 animals; they also line the stomachs and intestines of all 

 animals which possess them. The individual cells are termed 

 epithelial cells, and their height varies very much in relation 

 to their diameter. The height may be so small that the cell 

 appears like a flat tile, or it may be so great that the cell 

 is a pillar. Where the matter has been most closely investi- 



