DIFFERENCES BETWEEN ANIMALS AND PLANTS. 15 



being alike composed of molecular, cellular, and fibrous 

 tissues. 



c. Chemical Composition. Plants, speaking generally, exhibit 

 a preponderance of ternary compounds of carbon, hydrogen, 

 and oxygen such as starch, cellulose, and sugar whilst 



Fig. i. Algae and Infusoria, a Ciliated zoospores of Confervas; b Ciliated zoospore 

 of Vaucheria ', c Volvox globator, a locomotive fresh-water plant ; dEuplotes charon, 

 one of the Ittfusoria. All greatly magnified. 



nitrogenised compounds enter more largely into the compo- 

 sition of animals. Still both kingdoms contain identical or 

 representative compounds, though there may be a difference 

 in the proportion of these to one another. Moreover, the 

 most characteristic of all vegetable compounds viz., cellulose 

 has been detected in the outer covering of the Sea-squirts, 

 or Ascidian Molluscs; and the so-called "glycogen," which is 

 secreted by the liver of the Mammalia, is closely allied to, if 

 not absolutely identical with, the hydrated starch ot plants. 

 As a general rule, however, it may be stated that the presence 

 in any organism of an external envelope of cellulose raises a 

 strong presumption of its vegetable nature. In the face, how- 

 ever, of the facts above stated, the presence of cellulose can- 

 not be looked upon as absolutely conclusive. Another highly 

 characteristic vegetable compound is chlorophyll, the green 

 colouring - matter of plants. Any organism which exhibits 

 chlorophyll in any quantity, as a proper element of its tissues, 

 is most probably vegetable. As in the case of cellulose, how- 

 ever, the presence of chlorophyll cannot be looked upon 

 as a certain test, since it occurs normally in certain un- 



