Eeactioxs and Peoducts in Interspecific Crosses 



171 



fertility than is found in later matings, although at no time does the fertility 

 become equal to that in pure stock matings in any of the species. 



In any combination between these three species there is never entire infertil- 

 ity in any line found thus far in nature. I have recorded in table 22 only mat- 

 ings in which copulation was observed or known to have taken place, but in these 

 matings there are instances in which there is no copulation of the pair and they 

 pay no attention to one another. These cases have their causes in the breeding 

 reactions of the parent species and are in part instinctive reactions dependent 



Table 22. 



upon sex-attractions of one kind or another, most commonly that of odoriferous 

 secretions and possibly to other agencies. 



I have been most successful in the crossing of these species if they are mated 

 at the height of the first reproductive activity, at which time the instinctive reac- 

 tion against an outcross seems easiest to overcome, aided perhaps by the pres- 

 sure of accumulated reproductive elements within. My data show that in 

 these species there is at the start infertility such that only a small proportion of 

 the matings give adult progeny and that continued existence under the same con- 

 ditions results in the raising of this fertility to a considerably higher percentage 

 in the matings, but never entirely reaches the fertility of the matings within 

 any of the species. 



