163 The Mechanism of Evolution" in Leptinotaesa 



mately complete account of the analysis of the intercrossing of these two species, 

 but the complexity of the dissociation has made it largely a practical matter of 

 inadequate facilities. 



Both of the species are stable and constant and even under extreme changes of 

 the environment they retain their stability, altering only characters if at all, 

 but in combination in crossing the lines that have been experimented upon show 

 no end of diversity. Constant conditions surrounding the cross reduce or elim- 

 inate the dissociation of the gametes, the reaction appearing as simple, but 

 with ranging conditions in the medium the disruption is extreme. It may be 

 objected that in reality only a few character agents are involved, and this may 

 be true ; but there are some agents, that are specific and localized, capable of sep- 

 aration and recombination through the reactions of crossing plus the conditions 

 of the medium, so that it makes little difference what is personified or symbol- 

 ized to express our experiences. The important point is that these unseen 

 agents react precisely and orderly. In this series there are many color-con- 

 ditions, especially of the hypodermal colors, that are unstable and break down 

 at death, but which are nevertheless distinct and precise in life, and react 

 as distinct contrasting units of operation. I am aware that the color-producing 

 molecules may well be the same in all, and that the color differences may be 

 only differences in the arrangement of the component atoms and atom groups 

 of the molecules; but there is some precise cause of this. 



The result of the crossing of these two species under ordinary conditions may 

 be characterized as a collision between them, with disruption of each of the 

 gametic systems into fragments of different sizes and composition, which are in 

 form and position to be built into new positions and arrangements, so that the 

 results of a cross of this order might be the production of many different lines 

 of descent. It is the antithesis of the reaction of signaiicollis X divcrsa, where 

 the systems were not disrupted at all. The experience is suggestive of what 

 might conceivably happen in nature and be productive of some of the groups of 

 related species that occur, where lines of demarcation are wanting or difficult 

 to draw. It would be impossible to decide whether in any instance in nature 

 where there was extensive heterogeneity it is due to this or some other cause, for 

 the reason that the production of the condition would soon pass away, leaving 

 behind only the heterogeneous population, in which in nature nothing is known 

 as to the relations in breeding or in genetic reactions of the component elements. 

 I have put this to test in experiments described in a later part of this report. 



Whether all cultures of decemlineata crossed with all cultures of oblongata 

 would give this result I do not know. I have tested only crosses of my 99 

 decemlineata stock and oblongata from Temisco and Cuautla. They may 

 well be local differences in these species, such that the reactions of other sources 

 of materials would not be as complex as I have found them, or might be more so. 

 Whatever the solution of this problem may be, the relation between the two 

 species will not be any simpler than I have found it, and probably is much more 

 complex, taking the species as a whole, so that the potentiality for heterogeneity 

 between these two is very great. 



This cross reminds one strongly of some of the events that may have happened 

 in the production of the diverse strains of domesticated plants and animals. 

 Many garden fruits and flowers, dogs, poultry, and pigeons show endless 

 combinations of character that are present in the wild originals; and also 



