EXISTING ORGANISMS— CLASSIFICATION 



31 



in the muscles, nerve cells with long fibers which coordinate the 

 various organs, and many more (Fig. 13). Wherever found and 



Fig. 13. — Various kinds of cells. A, ovum of cat; B, spermatozoon of a snake; 

 C, ciliated epithelium from the digestive tract of a mollusc; D, cartilage of a 

 squid; E, voluntary or striated muscle fil)er from an insect; F, involuntary 

 or smooth muscle fibers from the bladder of a calf; G, nerve cell from the 

 human brain; H, white blood cell of frog; I, red blood cell of frog; J, same, 

 edge view; nu, nucleus. (From Woodruff, after Parker and Haswell, H, I, 

 J; and Dahlgren and Kepner, A-G.) 



