282 D. F. JONES. 



Darwin knew of many cases of total self-sterility and was so 

 convinced of the necessity for cross-fertilization that he was easily 

 persuaded from these observations that a prepotency of pollen 

 from unrelated plants did exist since he supposed this enabled 

 a plant to choose between its own and unrelated pollen when 

 both were brought at the same time to the stigmas by insects or 

 other agencies. So plausible have been the arguments in favor 

 of such an assumption that the prepotency of germ cells from 

 individuals of somewhat different constitution, even where com- 

 plete self-fertility exists, has been accepted as an established fact 

 and incorporated in textbooks on biology. 



Similarly inconclusive experiments have been performed with 

 animals. Marshall (1910) artificially impregnated a pure bred 

 dog with a mixture of equal quantities of seminal fluids from the 

 same breed and from a mongrel of unknown ancestry. Of the 

 four young which resulted one died early, and three resembled 

 somewhat the mongrel sire. Marshall cites another instance 

 in which a dog copulated with a member of the same breed and 

 two days later with a sire of different type. Out of three puppies 

 one was pure bred and two half-breeds. These cases, according 

 to this writer, indicated a selective action favoring dissimilar 

 rather than related spermatozoa. King (1918) mentions some 

 preliminary experiments with albino and wild gray rats in which 

 advantage was given to the former, yet the results tended to 

 show a prepotency of the latter, so that there was apparently a 

 selective action favoring the out-cross. The details of these 

 experiments are not given. 



In attempting to determine whether or not a selective action 

 exists small numbers can never be more than suggestive and 

 unless the mixture is applied at the same time to both types 

 furnishing the sperm cells there is no way of estimating the rela- 

 tive proportions of the two kinds of fertilizing elements present 

 in the mixture which are capable of functioning. Furthermore 

 a constant excess of cross-fertilized individuals over the others 

 may be due to the greater viability of the hybrids and hence 

 there will be a selective elimination of zygotes but not necessarily 

 slective fertilization. Hyde (1914) compared the matings of 

 different types of Drosophila within the strains and in reciprocal 



