232 HABITS AND INSTINCTS IN LEPTINOTARSA. 



this genus is thirty-five days, and yet I have often bred these long-lived adults 

 with the offspring of their own generation, and on several occasions with 

 those of the following generation. 



With other species of the genus, as, for example, multitamiata, oblongata, 

 iindecimlineata, dilccta, and signaticollis, the same results have been obtained, 

 excepting that there is a variation in the length of time that each species will 

 live. 



It is apparent that there is a high degree of difference between the species 

 of the genus in their ability to resist the abnormal condition of not being able 

 to reproduce at the proper time, and that this resistance is greatest in those 

 species which are from habitats where there is a great chance of unfavorable 

 conditions, as, for example, from the plateau of Mexico, where local condi- 

 tions may make necessary the prolongation of the reproduction period. In 

 the species decemlineata, inultitivniata, and oblongata this ability is developed 

 to a marked degree, and these species live in habitats where the conditions of 

 existence are much more variable than are those of the species dilecta, unde- 

 cimlineata, or violescens, which do not show as much resistance along this 

 line. This ability to hold in abeyance the reproductive capacity for longer or 

 shorter periods of time is characteristic of the entire genus ; it is quite possible 

 that it is an adaptation which has been preserved by selection, but I do not 

 believe it could have been caused thereby. Of course, if one is credulous 

 enough to accept Weismann's doctrine of germinal selection he might con- 

 sider that the whole phenomenon has been originated and controlled by select- 

 ive processes. If it is an adaptation, it is one that is not yet fully formed, in 

 that some of the individuals of the species do not show the slightest ability to 

 resist the prevention of their reproductive activities. However, such a char- 

 acter does offer an opportunity to test the possibility of creating experiment- 

 ally by selection an adaptation to changed conditions of existence ; because if 

 in experiment one could create a race in which all the individuals possessed 

 this capacity, it could not be considered in any other light than as an adapta- 

 tion developed in the species to enable it to meet unfavorable conditions in its 

 environment at the time of its normal reproduction. 



The importance of a habit like this to the species living upon the Mexican 

 Plateau, for example, is very great. In the North Mesa it often happens that 

 when a slight rain occurs in the spring these beetles emerge from aestivation, 

 and then there is no more rain for weeks. Inasmuch as very circumscribed 

 conditions are necessary for successful reproduction, it results that unless the 

 species is able to meet these suddenly introduced unfavorable conditions it is 

 exterminated. It is here that the habit which we have been discussing would 

 be of value for the purpose of preventing a wholesale destruction of the spe- 

 cies. Furthermore, only those individuals which possessed this trait would 

 be able to survive and reproduce, and thus the character would be preserved 



