20 DIFFERENCES BETWEEN ANIMALS AND PLANTS. 



organic parts enlarge, as is distinctly seen in the cells of the 

 epithelium, in the muscular fibres, and in the primary fibrous 

 fasciculi of the nerves ; whilst mere nuclei, as the blood, 

 lymph, or pus-globule, remain, or suffer diminution in the 

 course of farther development.]* 



SECTION III. 



DIFFERENCES BETWEEN ANIMALS AND PLANTS. 



57. AT first sight, nothing would appear more widely 

 different than animals and plants. What is there in common, 

 for instance, between an oak and the bird which seeks shelter 

 amidst its foliage ? 



58. The difference, indeed, is usually so obvious, that the 

 question would be superfluous, if applied only to the higher 

 forms of the two kingdoms ; but as we descend to the simpler 

 and therefore lower forms, the distinctions become so few, and 

 so feebly characterized, that it is at length difficult to pronounce 

 whether the object we have before us is an animal or a plant. 

 Thus, the sponges have so great a resemblance to some polyps, 

 that they have generally been included in the animal, although 

 in reality they belong to the vegetable kingdom. f 



59. Animals and plants differ in the relative predomi- 

 nance of their component elements, oxygen, carbon, hydrogen, 

 and nitrogen. In vegetables, only a small proportion of nitro- 

 gen is found, while this element enters largely into the com- 

 position of animal tissues. 



60. Another peculiarity of the animal kingdom is the 

 presence of large, distinctly limited cavities, for the lodgment 

 of certain organs ; such is the skull and the chest in the higher 

 animals, the branchial chamber in fishes, and the abdomen 

 or general cavity of the body, which exists in all animals, with- 

 out exception, for the reception of the digestive organs. 



61. The well-defined and compact forms of the organs 

 lodged in these cavities is a peculiarity belonging to animals 

 only. In plants, the organs designed for special purposes are 

 never embodied into one mass, but are distributed over various 

 parts of the individual ; thus the leaves, which ansvrer to the 



* Wagner's Physiology, p. 221. 



f The animality of sponges is maiutained by some of our most dis- 

 tinguished naturalists. ED. 



