92 



The Source of Variability 



GUIARDI 



SINENSIS 



PHILIP! 



Fig. 38. A structure of the male genitalia of selected species in the mosquito 

 Cidex pipiens line. The basal species C. sinensis is a member of a primitive, 

 closely related line and is added for purposes of comparison. Upper two rows, 

 lateral aspect; lower two rows, ventral aspect. (Modified from Barraud, Ed- 

 wards, and others.) 



system of developmental enzymes which produces a leg. Further- 

 more this change has occurred in one jump, or mutation. The best 

 explanation to date is that the mutant represents some simple 

 switch in physiological pathways early in ontogenetic development. 

 In nature, several cases suggest some such mechanism as the cause 

 of new characters. 



