282 



cles. Jn Ihc leaf-hoppers on t'he other hand there seems Httle 

 chfference in this respeet, prolKi1)ly due to the faet that tiie 

 thoracic muscles are already somewhat feeble and little adapted 

 for strong flight. 



In polymorphism there are two well marked forms, t'he ex- 

 tremes, that is, of macropterism and brachyptcrism, as well as 

 numerous intermediate forms sometimes. 



In older times, it was supposed that the hrachypterous (or 

 apterous) forms were sexually immature, and later, w'hen niac- 

 ropterous and apterous forms were observed in copulation, it 

 was supposed that they were nymphs capable of procreation. 

 These apterous or brac'hypterous forms 'have been reared from 

 ordinary nymphs and are completely mature as regards their 

 sexual apparatus. 



The genus Perkinsiella aiifords a good example. There are 4 

 known species, closely allied but abundantly distinct. Two oc- 

 cur in Australia (one also in Hawaii) one in Viti, one in Java; 

 the first three have been abundantly investi'gated by Koebele 

 and Perkins, the fourth by Breddin. 



(1) saccharicida Kir'kaldy: the males always macroptcrous, 

 the female is di- (or more or less poly-) morp'hic. ^ 



(2) i^rainiiiicida Kirkald}' : as far as known the male is always 

 macroptcrous. the female brachypterous. 



(3) -c'ificjisls Kir'kaldy: both sexes are dimorphic pterygially. 



(4) z'asfatri.v jireddin : similar to ^7'/;V//.s-/.s\ 



It has been supposed by Flor and Sahlberg that this poly- 

 m()rphism is caused by climatic influence. These authors be- 

 lieve that this inability to develop properly the tegmina and 

 wings, does not exist embryonically in t'he egg, but depends on 

 accidental conditions, such as the nourishment of the nymphs, 

 and above all on the state of the climate during their develop- 

 ment. Sablberg adds that the 'feeble development of the organs 

 of flight is altogether due to the greater develooment of the 

 other organs of motion, i. e., t'he legs. Renter believes, how- 

 ever, that the increa'se in number of polymorphic species as one 

 proceeds northwards in Europe dei^ends probablv on many 

 other causes, independent of climatic influence. Thus only 

 cig'ht species of Auchenorhynchi live in Lapland on trees or 

 bushes, and these species are always monomorphic. 



Renter makes the following observations: 



(i) Dimorphic forms are found even in the tropics. 



(2) S'hort-winged individuals are observ^ed most fiecjuently 

 among insects whose legs are well developed and constructed 



