16 A PRIMER OF BIOLOGY 



rated there to motile organs muscles acting at 

 some times on a jointed skeleton, and thus giving 

 the entire organism the power of locomotion or 

 permitting of movements in individual parts of the 

 body. At other times the central nerve impulses 

 are transmitted to glands, inducing or regulating 

 secretion in or from them. Briefly put, the whole 

 organism is sensitive in every part and capable of re- 

 sponding to stimuli of many different kinds. Further, 

 in this case we are entitled to assume that the 

 frog is able to analyse the impulses by which it 

 is affected, that it is " conscious " of them ; at all 

 events we recognise that sensitivity has reached 

 a higher stage in development than it has in 

 Vaucheria. 



It is quite unnecessary for us at present to go into 

 further detail by way of illustration ; it will be suffi- 

 cient if we have learned to recognise in all organisms 

 the power of self-nourishment, the power of reproduc- 

 jummary. tion, and the power of receiving and responding to 

 stimuli and if, further, we have recognised that these 

 powers are manifested by very different mechanisms 

 iu the plant and in the animal worlds. We must 

 also note that the green plant, even one so low in 

 the scale of life as Vaucheria, must manufacture its 

 organic food from inorganic constituents derived from 

 the soil, water and air, before it actually employs 

 such food as nutriment for its protoplasm, while the 

 animal absorbs organic materials already manu- 

 factured ; that plants (although not all plants) have 

 both a sexual and an asexual method of reproduc- 

 tion, while animals (with relatively few exceptions) 

 possess the sexual method only ; and lastly, that 

 plants are much less obviously sensitive to impulses 

 from without than are animals. This last charac- 



