25O WILLIAM LAWRENCE TOWER. 



(1) Assuming that the phylogenetic picture that we have 

 drawn of the three species is essentially correct, and that L. 

 decem-lineata is the younger derivative from the Mexican types, 

 an essentially fair conclusion as far as conclusions in this line 

 are at all possible, then the results of the tests show that there 

 is a dominance of the older phylogenetic condition over the 

 newer; or 



(2) It may be concluded that in the origination of L. decem- 

 lineata in its northern range, there had been a loss of an agent 

 in the organization, which when present, produced retention 

 and slow loss of water under desiccation, and its absence ease of 

 loss, the experimental tests showing, therefore, the dominance 

 of the presence over the absence. In that the reaction in crossing 

 is a monohybrid one, one unit of difference may be assumed; or 



(3) It may be concluded that we are dealing with a physical 

 state in the living mechanism that exists as two conditions, 

 alternative to one another in crossing reactions, but, which by 

 the pressure of the medium may be altered to present first one 

 aspect of its reaction, and under other conditions of the medium, 

 the opposite aspect of its effect in the reactions of the living 

 mechanism. 



Which of the three possibilities is chosen as the correct one 

 will depend entirely upon one's philosophical background, and 

 from each a rather entertaining and plausible argument can be 

 made. From purely mechanistic and physico-chemical con- 

 siderations of living phenomena, I am inclined to the third 

 possibility, as not only the more probable and thinkable, but 

 also the one that as a working hypothesis offers the only opening 

 for further experimental investigation. 



In this preference I am no doubt prejudiced in my choice 

 by many experiences with the behavior of the non-hibernating 

 generation in which the behavior is easily, rapidly and positively 

 altered, reversed at will by changes in the water content of the 

 medium, producing reversibility of many of the trophisms of 

 that generation. However, in this first summer generation, 

 another condition of the reproductive cycle is under observation, 

 and in that the reproductive cycle itself is present in two sharply 

 alternative conditions, to breed or not to breed, activity or 



