GRASS THRIPS. 53 



The mesothorax, figs. 6 and 14, msth, is, in the adult, about 

 twice as long as either of the other thoracic somites. In the 

 larva and pupa it is not proportionately so long. It is shaped 

 like a barrel, except that it is thinner dorsoventrally at its ante- 

 rior end. In the winged form it bears the wings, and in the 

 wingless forms it is either smooth or bears the rudimentary 

 wings. In the former its dorsal surface is broken up into a num- 

 ber of plates which allow for the movement of the wings. 



The metathorax, figs. 6 and 14, mtth, is narrow in front and 

 broadens out behind to join the abdomen. On its dorsal surface 

 it has the appearance of being an abdominal rather than a tho- 

 racic somite. 



Each of the three thoracic somites bears a pair of legs that 

 have the usual number of joints. All of the joints, except the 

 coxa and tarsus, are flattened laterally, fig. 16. The tarsus has 

 at its extremity, in place of the usual claws, a bladder shaped 

 organ, fig. 16, at the sides of which there are two small rudi- 

 mentary organs that many entomologists interpret as being tar- 

 sal claws. The bladder is supposed to represent modified 

 pulvilli. 



The anterior pair of legs are quite short and stout, and are 

 attached near the anterior part of the somite. The second pair 

 of legs are somewhat longer and are attached to the posterior 

 part of their somite. The third pair of legs are much the longest 

 and slimmest of the three pairs. They are attached to the ante- 

 rior part of the somite. 



The abdomen is made up of eight somites. It tapers gradually 

 from before backward, the last somite being quite slender. The 

 first five somites are nearly alike in shape. The sixth somite is 

 wedge shaped with its broad end placed on the dorsal surface 

 and its edge on the ventral surface, fig. 14. 



The ovipositor is attached at the junction of the sixth and 

 seventh abdominal somites and when not in use fits into a small 

 groove on the ventral surfaces of the seventh and eighth somites. 

 It is made up of four valves, fig. 14, ovp, which are united so as 

 to leave a groove on the dorsal surface, down which the eggs 

 pass at the time of oviposition. The three angles of the oviposi- 

 tor are sharply serrate, so that it will hold, while being worked 

 into the tissues of the plant. 



