DIFFERENCES BETWEEN ANIMALS AND PLANTS. 21 



to have been referred to that division of the Protozoa. This 

 is also the case with some adult plants, such as Volvox 

 glob at or (fig. 3). 



Fig. 3. Algse and Infusoria, a Ciliated zoospores of Conferva; b Ciliated zoospore 

 of Vaucheria ; c Volvox gk>ba.tor, magnified ; d Euplotes Charon t one of the 

 Infusoria, magnified. 



b. Internal Structure. Here, again, no line of demarcation 

 can be drawn between the animal and vegetable kingdoms. 

 In this respect all plants and animals are fundamentally 

 similar, being alike composed of molecular, cellular, and 

 fibrous tissues. 



c. Chemical Composition. Plants, speaking generally, ex- 

 hibit a preponderance of ternary compounds of carbon, 

 hydrogen, and oxygen such as starch, cellulose, and sugar 

 whilst nitrogenised compounds enter more largely into 

 the composition 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 com- 

 pounds 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 of plants. As a general rule, how- 



