THE PRIMARY TISSUES 523 



constitute a net-work of cells, that communicate 

 with each other throughout the body. 



But as the elementary composition of animals 

 is more complex than that of plants, they pre- 

 sent a more diversified system of organization, 

 if we except the lowest species of zoophytes, 

 which so nearly resemble the simpler micro- 

 scopic plants, that some physiologists have 

 maintained their mutual convertibility into 

 each other. For example, in addition to cellular 

 tissue that forms the basis of plants, and the 

 principal portion of the higher animals, the 

 latter are composed of muscular and nervous 

 tissues, by which they are endowed with the 

 powers of locomotion, perception, and con- 

 sciousness. The muscular fibres are formed of 

 fibrin, the particles of which have been said not 

 to exceed the 40.000th part of an inch in 

 diameter, and are arranged in lines that re- 

 semble rows of globules under the microscope ; 

 while the nervous tissue is composed of albumin, 

 and certain oily matters that contain much hy- 

 drogen, and a little phosphorus, forming an in- 

 finite number of exceedingly minute and de- 

 licate tubes. (Miiller's Elements of Physiology, 

 p. 599.) 



By the union of these three primary tissues 

 in various proportions, the different complicated 

 organs of the animal fabric are built up, as the 

 heart, stomach, intestines, liver, pancreas, kid- 



