126 INSECT TRANSFORMATION 



saw-flies (Cephidae) the thoracic legs of the larva are reduced 

 still further than those of the Sirex grub, being only minute, 

 unjointed processes. 



Thus we may pass naturally from these tunnelling grubs 

 with their vestiges of legs to the larvae of the great majority 

 of the Hymenoptera gall-flies, ichneumon-flies, wasps, bees, 

 ants in which legs are entirely wanting. A bee grub for 

 example (Fig. 71) has an extremely soft, flexible cuticle, less 

 wrinkled than that of a legless beetle grub, and becomes 

 markedly swollen as, after each moult, it imbibes more and 

 more of the rich food wherewith it is furnished. The head 

 appears disproportionately small in comparison with the body, 

 as the larva increases in size and usually becomes bent on 



FIG 71. STAGES OF THE HONEY-BEE (AptS 



a, young larva ; b, full-grown larva ; c, pupa (side views). 

 X3. After Phillips, U.S. Dept. Agric., Farmers' Bull. 447. 



itself, with the ventral aspect concave. A peculiarity in the 

 inner structure of these legless hymenopterous grubs is that 

 no waste matter is passed from the food-canal until shortly 

 before pupation, either there is no anus, or there is no con- 

 nexion between stomach and hind-gut until the last stage of 

 larval life. 



The legless type of larva, represented as we have seen among 

 some families of beetles and many sections of the Hymenoptera, 

 is characteristic of the whole order of two-winged flies (Diptera) 

 within which it shows very marked modifications in detail. 

 The structure of the adult Diptera is very highly specialized. 

 The fore wings only are developed for flight, the reduced 

 hindwings being modified into small balancing organs (halters), 

 and the thorax, dominated as it were by its middle segment, 



