SPONTANEOUS GENERATION 67 



While it is impossible to draw a definite line between animals 

 and plants it is possible, nevertheless, through the sum of char- 

 acters to determine whether an organism is either plant or 

 animal, or some form of life intermediate between them. For 

 the determination of a given questionable type it is necessary 

 to take into consideration not only form, movement, and mode 

 of nutrition but also the immediate relations. Thus Euglena 

 has many of the physiological characteristics of plants of which 

 the mode of nutrition is the most important; but it itself and a 

 nearly-related type, Chromulina flavicans, have the power of 

 both holophytic and holozoic nutrition and can live in the dark 

 on solid protein matter, or in the light without solid food where 

 it manufactures its food. An allied form, Astasia, lives solely 

 on solids. The structures and life history of Euglena place it 

 unmistakably with the animal flagellates. 



It is now known that plants, like animals, renew their proto- 

 plasm with oxygen, salts and proteins, and give off C0 2 and 

 other waste matters the same as animals do, the only essential 

 difference being their power to manufacture the proteins to be 

 used as food. Their functions, therefore, are fundamentally 

 constructive while animals are destructive; all plant tissues 

 and organs are differentiated to subserve this great function 

 while those of animals are mainly differentiated for the pro- 

 curing of food, digesting and assimilating it. The two great 

 lines of living things have thus developed in different directions, 

 and the higher we go in either scale the more easily we are able 

 to distinguish between animals and plants by these structural 

 differences. 



Spontaneous Generation. "But expectation is permissible 

 where belief is not; and if it were given me to look beyond the 

 abyss of geologically recorded time to the still more remote 

 period when the earth was passing through physical and chem- 

 ical conditions which it can no more see again than a man can re- 

 call his infancy, I should expect to be a witness of the evolution 

 of living protoplasm from non-living matter." (Huxley, Bio- 

 genesis and Abiogenesis.) 



All biologists are practically agreed that living matter origi- 



