Eeactions and Products in Interspecific Crosses 123 



hition ; and in the laboratory, if it alone had been seen, an easy interpretation 

 would have been that one parent was homozygous, the other heterozygous, for 

 some character or agent. Case 3 and case 4 show the remainder of the relations 

 and the complexity of the actual series. 



The essential agent in the entire series beyond question is the Ac determiner, 

 and its changes with the change of environment of the stocks, its capacity 

 to be altered rapidly in experiment, and the limits of change that it shows in 

 both of the species. It is clearly, in its operation to the conditions in the 

 medium, closely and accurately balanced, and especially to the relation of 

 water-loss in the organism and the consequent change in the relations and 

 associations of the agent productive of elytral color marks and pattern. That 

 the Ac determiner is a specific agent in the gametic complex is shown by its 

 limits in any one species that are specific for that, and by the fact that it is not 

 capable of replacement in the complex by the corresponding agent from another 

 source, thus giving in materials that are visibly the same, different Ac value 

 ranges and different lengths of ontogeny, the present measure of the Ac deter- 

 miners reaction value. Every indication regarding the nature of the Ac agent 

 tends to show that it is a property of the whole, a cytoplasmic determiner, and is 

 a condition of the material rather than any specific substance or body, but its 

 action is important in the life of the species and active in the production of dis- 

 turbances in the gametic system, when present in differing rates or reaction, 

 in any zygote. Another peculiarity is its tendency to change rapidly in cross- 

 ing within its limits to a common value of operation in Fg. As a gametic agent 

 it is a very delicate one, easily neglected, but able to produce wide differences 

 in the results of crossing, so that one is made to ask to what extent an agent of 

 this character may have played the role of confusing us in some of the Mende- 

 lian reactions, leading to the assuming of conditions in the materials that were 

 not really there at all. Throughout this series it is certain that when the Ac 

 values are like, the conditions of the medium do not within limits have any 

 action upon the reactions in crossing these two organisms, the resultant arrays 

 being in all portions of the series entirely the product of the gametic constitu- 

 tions present. 



Eather interesting in the series is the tenacity with which each of the gametic 

 systems retains its entirety. There are in this series no instances of the crossing 

 of agents from one gametic system to the other, although there are plenty of 

 opportunities for this to happen, so that the entire reaction is a most typical 

 monohybrid one. At no point is there indication of difference in this cross in its 

 reactions from those found and described in other monohybrid crosses. How- 

 ever, "monohybrid crosses" represent to me more a type of reaction than an indi- 

 cation or statement of the differences present in the crossed lines. In this 

 instance there are plenty of differences that in all stages might have become disso- 

 ciated from the original association and formed attachments to other systems 

 present in the germinal material during gametogenesis. In some respects this 

 series of experiments is different from the crossing of many domesticated races, in 

 that in many of these there is only one species base to which are attached the 

 agent or agents that are capable of displacement and rearrangement. In the 

 signaticollis x diversa series, the total gametic complex acts as a unit in the oper- 

 ations of gametogenesis. Both are the same in action, differing only in the 

 character and magnitude of the unit systems that are engaged in the operations. 



