184 THE BREEDING OF ANIMALS 



171. The significance of conjugation and fertilization. 

 The real purpose of fertilization is not well under- 

 stood. Biologists are not yet able to speak with positive 

 assurance as to the real character of the actual biological 

 phenomena which result from conjugation of the male 

 and female germ-cells. Butschli believed that fertiliza- 

 tion was a process of rejuvenation. This idea involves 

 the assumption that the union of the germ-cells of two 

 weak individuals will result in the production of a strong 

 individual. 



Jennings, in a series of very skillful and carefully con- 

 trolled experiments with paramoecium, found that after 

 conjugation the rate of division was not accelerated but 

 was actually slower. Paramoecium which had been 

 artificially weakened and their rate of division retarded 

 when allowed to conjugate was not in most cases bene- 

 fited. Some were apparently benefited, but in all cases 

 the rate of division was slower than in cultures in which 

 the paramoecium was well nourished. In other words, 

 conjugation was of advantage to some and not to others. 

 Jennings concluded that conjugation is for the purpose 

 of bringing about a recombination of characters. Some 

 of them are very beneficial and will persist and multiply, 

 others are disadvantageous and these will fail to live and 

 reproduce. The combinations most likely to persist 

 are heterozygous. 



As Morgan l has explained, " The meaning of conjuga- 

 tion, and by implication, the meaning of fertilization in 

 the higher forms is from this point of view as follows : 

 In many forms the race, as a whole, is best maintained 

 by adapting itself to a widely varied environment. A 

 heterozygous or hybrid constitution makes this possible, 



1 Morgan, "Heredity and Sex," p. 12. 



