GENERAL ZOOLOGICAL FACTS AND THEORIES 287 



b. Theories 

 (i) Heredity 



THE INHERITANCE OF ACQUIRED CHARACTERS. Up to the 

 middle of the nineteenth century biologists quite generally believed 

 that acquired characters are inherited. Lamarck in his " Fourth 

 Law of Evolution " says: " All that has been acquired, begun or 

 changed in the structure of individuals in their lifetime, is pre- 

 served in reproduction and transmitted to the new individuals 

 which spring from those which have inherited the change." 

 Darwin accounts for many adaptations by the inheritance of 

 acquired characters. Many controversies arise because of mis- 

 understandings as to what really constitutes an acquired charac- 

 ter. Parts of a man's body may become changed by use or dis- 

 use, e.g. the arm of a blacksmith reaches a size above the normal 

 because of constant use. If this characteristic influences the 

 germ cells of the blacksmith, and reappears in his offspring, we 

 have an illustration of the transmission of an acquired character. 



Weismann (278) is the foremost opponent of the belief in this 

 theory. He led scientists to examine critically all reported cases, 

 and as a result it was found that no case really shows that a charac- 

 ter was not inborn instead of acquired. Mutilations, such as the 

 severing of the tails of sheep, have been practiced for countless 

 generations without affecting the tailed condition of each succeed- 

 ing generation. Many supposed cases of the inheritance of 

 characters produced in individuals by climatic or other external 

 factors are nothing more than the effects of the external stimuli 

 upon the developing organism. For example, certain snails if 

 reared in small vessels of water develop into small adults, but 

 if the eggs of these dwarfs are allowed to develop and the larvae 

 to grow to maturity in a large vessel of water, the normal size 

 is regained. 



It seems probable that whenever an organism is changed by 

 its environment and the change is transmitted to its offspring, 



