INSECT TRANSFORMATION 



of two short basal segments and a third elongate and stiff, 

 suggesting a fine bristle. 



In the mayfly's thorax the first segment is small, the second 

 segment (mesothorax) dominating this region of the body and 

 bearing a pair of wings, subtriangular in shape and relatively 

 ample in extent, with a nervuration in which all the typical 

 longitudinal trunks are usually present, while numerous 

 cross-nervules make a complex network. The third segment 

 (metathorax) is short, the hindwings being small, with the 

 nervuration somewhat reduced. The legs are relatively long 

 and slender, the number of foot-segments being very variable 

 from one to five ; in some male mayflies the forelegs are 

 of exceptional length. 



FIG. 51. MAYFLY (Ephemera). 



A, male; B, nymph. Side view. Somewhat enlarged. From Comstock 

 " Introduction to Entomology ", after Needham. 



The abdomen is elongate and narrow with a pair of long, 

 jointed tail-feelers (cerci) on its tenth segment and, in some 

 genera, a median jointed process between these. It has been 

 stated that a mayfly takes no food ; nevertheless its digestive 

 tube is present with the normal regions gullet, crop, stomach, 

 and intestine recognizable. The walls of this food-canal 

 are very thin, and the stomach becomes swollen with air which, 

 swallowed through the mouth, is confined by the action of valves 

 at either end of the mid-gut. The reproductive organs are 

 of a simple and primitive type, the paired oviducts of the female 

 opening separately to the exterior behind the seventh 

 abdominal segment, instead of passing into a median vagina, 



