320 



Scientific Froceedings, Royal Dublin Society. 



and tlie continuation of the acramic series may be shown m the following 

 way :— 



^ 



a.v 



(Sexuparae) 



(Sexuparae) 



WW 00 oo 



(Sexuparae) 



Klondnitzld found in Ajphis hederae Kalt., that the sexuparae are apterous 

 and the same mother produced both <? c? and + ° . 



Baker and Turner (1916) found in Aphis pomi De Geer, that the same 

 mother (sexuparae) could pi'oduce both sexes ; and in one case a mother 

 produced both sexes and agamic forms. 



One can also consider in the case of Aphis ritmicis that the same mother 

 can give rise to both sexes, in that the winged sexuparae, which produce only 

 sexual ° + , are presumably predestined in the original agamic mother to 

 produce sexual + ? . 



Similarly, both sexual and agamic forms are produced by the same 

 mother. 



From a colony of agamic apterous females — Beans B^ — all stages appeared 

 in October, namely 5" 3- , sexual ° + , a. v. + + , and w. v. + ° . 



In conclusion, it is seen that in my experiments sexual forms developed 

 under favourable conditions of food and temperature. They may arise in 

 different generations. They were produced under the low temperatui-es of 

 October in the glass-house, and later under the warm temperature in the 

 green-house. Further, agamic and sexual forms appeared together under the 

 same conditions of food and temperature. The autumn seasonal factor would 

 appear to be important in accounting. for the large numbers of sexual forms 

 produced at tliis period. It is difficult to believe that the influence of 

 external factors is the important one, when one considers that under the same 

 external conditions totally different forms are produced — namely, c? 6, 

 sexual 9 ? , and agamic females. Over long periods of time, external factors 

 associated with seasonal conditions would be important, and it appears 

 higlily probable that the parthenogenetic and sexual phases are adaptations 

 to seasonal conditions. 



While the generative changes appear to be determined by an internal 



