312 GENERAL ZOOLOGY 



indirect effect, through functional responses, in modifying 

 animals. (2) Organisms develop new structures and parts as a 

 result of need or necessity, i.e., new parts evolve to meet certain 

 requirements. (3) Use or exercise develops an organ, while dis- 

 use results in atrophy. (4) All characteristics or changes, 

 whether caused by environmental effects, habits, use or disuse, 

 are inherited. Lamarck's emphasis and elaboration of the prin- 

 ciple of the inheritance of acquired characters have resulted in 

 this principle being often referred to as the Lamarckian factor 

 in evolution, though as a matter of fact the idea was also held by 

 a number of his predecessors. 



Darwin. — Appointed naturalist of a British naval surveying 

 expedition, Charles Darwin, an Englishman, at the age of 22 sailed 

 from Plymouth on H.M.S. Beagle for a round-the-world voyage 

 that lasted five years. Most of this time (nearly four years) 

 was spent in coasting the Eastern and Western shores of South 

 America and it was in South America that Darwin first became 

 interested in evolution. There is every reason to believe that 

 Darwin left England firm in the conviction that species were 

 created separately and that he was converted from that view 

 by " certain facts in the distribution of organic beings inhabiting 

 South America, and in the geological relations of the present to 

 the past inhabitants of that continent." Darwin is outstanding 

 in the field of evolution because he was the first properly to 

 evaluate the data of morphology, embryology, and paleontology, 

 and to utilize the derived principles in the elaboration of an 

 explanation of evolution that anyone could understand. Save 

 for minor details, that have proved to be incorrect, Darwin's 

 theory of evolution has withstood the tremendous surge of 

 adverse criticism with remarkable success, all of which is a 

 tribute to the fundamental soundness of his work. Darwin 

 neither affirmed nor denied the possibility of the inheritance of 

 acquired characters. On the other hand, he appreciated the 

 greater importance of congenital variations and heredity in 

 evolution, and stressed them accordingly. Alfred Russel 

 Wallace, Herbert Spencer, Patrick Mathew, and others had also 

 recognized the importance of these factors, but none achieved 

 Darwin's success in welding these factors into a constructive 

 theory. Darwin published the results of his studies in a series 



