Animals and Plants. 177 



This single cell may, or may not (parthenogenesis), in both 

 require fertilization. Fertilization consists, in both plants and 

 animals, of the union of a small motile sex-cell (spermatozoon 

 or antherozoid) with a larger quiescent sex-cell, the ovum or 

 oosphere, the union in both being chiefly a union between the 

 nuclei of the respective sex-cells. 



These are some of the more important likenesses between 

 animals and plants, and it is obvious that they are so numerous 

 and so important that plants and animals must have come 

 originally from the same stock. 



Next for the essential differences. Plants and animals differ 

 in physiological characters as well as in morphological. 



I. Plants, as a rule, derive their carbon from the carbonic 

 acid of the atmosphere, by the help of chlorophyll, which is 

 generally prevalent in the vegetable kingdom ; the other sub- 

 stances which build up their bodies are absorbed as inorganic 

 salts from the soil, or from the water in the case of aquatic 

 plants. 



Animals, on the other hand, require as food organized 

 substances, living or dead protoplasm, animal or vegetable. 

 Even a creature so low in the scale as Ammba would starve 

 if kept in water that contained all the components of its 

 protoplasm in the form of salts in solution. It eats solid 

 particles of animal or vegetable matter. 



To this rule there are exceptions, both on the animal and 

 on the plant side. In the first place, there are animals with 

 chlorophyll and plants without it. Hydra viridis, certain 

 infusorians, etc., have chlorophyll, and can therefore obtain 

 carbon from the atmosphere. In the case of Hydra we may, 

 it is true, have to do with a symbiotic organism, but there are 

 infusorians in which the chlorophyll seems to be undoubtedly 

 an integral part of the animal. On the other hand, there are 

 the insectivorous plants and the non-chlorophyllaceous plants. 

 The insectivorous plants form a physiological assemblage of 

 dicotyledonous plants belonging to more than one natural 

 order, which agree in the fact that they possess various 

 mechanisms for the capture, digestion, and absorption of 

 insects and other small creatures. They produce a digestive 



