Pomona College Journal op Entomology 865 



BEITRAGE ZUR KENNTNIS DES (JENEHAIIOUSWECKSKLS HEI 



EINIGEN Al'IDID.E 



1. KLODNITSKI 



Zool. .hilirh. lid. XXXIII, Heft. 5. 1!)12. 



The species considfi-rd in icirtictilar are Siphonopora ro.sae, Aphis hederae, 

 A. saleceti, ('hartophonts lf'slii(li)i(il iis and ('. accris. There arc iiiimhtdus 

 diagrams and tables. The fieMcral results are as follows: 



Every one of the investin'at<'d aphid raees possesses a single particular 

 cycle which consists of partlienogenetic and sexual generations. The occur- 

 rence of the sexual animals and also tlie otlier characters of the cycle, (occur- 

 rence of the winged forms, rest ])eriods of eggs, etc.), arc dependent upon 

 inner causes. The outer factors can only lead to somatic changes, also to such 

 which consist of the check of dcveloiiment and various different {juantitativc 

 modifications, but they can call forth no generative changes, which modify 

 the method of propagation in ((ualitative regard. 



There are two particular types of cycles. In one group of individuals 

 with one year there is a complete and closed cycle. Under this come the sexual 

 animals for the most part, after a certain number of the parthenogenetic gen- 

 eration. The second group has an incomi)lete cycle whose geneological stems 

 can propagate themselves unbroken through a very long time by partheno- 

 genesis. From these stems the branches separate gradually, which end with 

 sexual animals. 



