224 LIFE AND HABIT. 



the slightest conceivable variations should le referred to 

 changed conditions, external or internal, and to their dis- 

 turbing effects upon the memory; and sterility, without 

 any apparent disease of the reproductive system, may 

 be referred not so much to special delicacy or suscep- 

 tibility of the organs of reproduction as to inability on 

 the part of the creature to know where it is, and to 

 recognise itself as the same creature which it has been 

 accustomed to reproduce. 



Mr. Darwin thinks that the comparison of habit with 

 instinct gives " an accurate notion of the frame of mind 

 under which an instinctive action is performed, but 

 not," he thinks, " of its origin." 



" How unconsciously," Mr. Darwin continues, " many 

 habitual actions are performed, indeed not rarely in 

 direct opposition to our conscious will ! Yet they may 

 be modified by the will or by reason. Habits easily 

 become associated with other habits, with certain periods 

 of time and states of body. When once acquired, they 

 often remain constant throughout life. Several other 

 points of resemblance between instincts and habits 

 could be pointed out. As in repeating a well-known 

 song, so in instincts, one action follows another by a 

 sort of rhythm. If a person be interrupted in a song 

 or in repeating anything by rote, he is generally forced 

 to go back to recover the habitual train of thought; 

 so P. Huber found it was with a caterpillar, which 

 makes a very complicated hammock. For if he took 

 a caterpillar which had completed its hammock up 

 to, say, the sixth stage of construction, and put it into 

 a hammock completed up only to the third stage, the 



