GENERAL ZOOLOGICAL FACTS AND THEORIES 289 



a group of molecules, among which are some of complex compo^i- 

 tion, and therefore of relatively considerable size " (278, p. 369). 



GALTON'S LAW OF ANCESTRAL INHERITANCE. Francis Galton, 

 from a study of pedigreed dogs and the genealogical records of the 

 British Peerage, came to the conclusion that in an organism of 

 bisexual parentage, " The two parents between them contribute 

 on the average one half of each inherited faculty, each of them 

 contributing one quarter of it. The four grandparents contribute 

 between them one quarter, or each of them one sixteenth; and so 

 on, the sum of the series -J- + \ + i + TO + being equal to 

 i, as it should be." It has been demonstrated that this law is 

 only an approximation of the real result (241). 



MENDEL'SLAW OF INHERITANCE (227). The results of Mendel's 

 experiments in hybridizing peas and other plants were published 

 by him in 1866, but did not receive any attention from biologists 

 until 1900, when they were discovered in an obscure periodical 

 by several botanists. Since the latter date, Mendel's law has 

 become a favorite object of investigation with both botanists and 

 zoologists, until now its complexities are so great as to make the 

 details of the subject unintelligible except to persons working in 

 this particular field. 



An outline of one of Mendel's experiments will serve to illus- 

 trate his law (269). The varieties of the edible pea were se- 

 lected by him for hybridization. When a tall pea was crossed 

 with a dwarf pea, all of the offspring were tall. " Tallness," 

 therefore, is said to be a dominant character (D) and "dwarf- 

 ness " a recessive character (R). 



When the hybrids were allowed to fertilize themselves, three 

 fourths of their offspring were tall (D) and one fourth dwarf 

 (R) ; there were no intermediate forms. When these dwarfs were 

 allowed to fertilize themselves, only dwarf offspring resulted. 

 When the tall peas were allowed to fertilize themselves, one third 

 of them produced tall offspring, which when inbred produced 

 only tall peas; the other two thirds when inbred produced three 

 fourths tall (D) and one fourth dwarf (R) offspring. The result 



