THE PEAB THRIPS IN CALIFORNIA. 23 



the pear thrips is curved downward. The passageway between the 

 plates is grooved so that the eggs can pass through readily. The 

 upper edge (of the upper plates) is fitted with sharp sawlike teeth, 

 while the lower plates have similar teeth for most of the way but 

 also boar a number of broad cutting teeth. The end of the ovi- 

 positor is sharp and pointed. When this is inserted into the plant 

 tissues, the slit or opening is enlarged by the action of the hard ser- 

 rate edges of the ovipositor as it is worked up and down by the 

 rather powerful muscles of the abdomen. The ovipositor when not 

 hi use is protected in a sheath along the ventral side of the last two 

 segments of the abdomen. 



WINGS. 



The wings are long and slender, membranous, with a fringe of 

 fine hair upon both the anterior and posterior margins, and are never 

 folded. Both pairs of wings are quite similar and when at rest are 

 laid back flat upon the abdomen, the pairs lying parallel in the Tere- 

 brantia. The wings of the family Thripidse, to which the pear 

 thrips belongs, are slender, and taper from the base to the tip, which 

 is pointed; they bear a general resemblance to sabers. The veins 

 in the family Thripidas are not so prominent as in the family iEolo- 

 thripidse, and only one or two longitudinal veins are present, the 

 cross-veins being very obscure. 



FEET. 



The legs and feet of thrips form one of the chief characteristics 

 which separate this order from the various other orders of insects. 

 They are composed of the usual parts of an insect leg, namely, coxa, 

 trochanter, femur, tibia, and tarsus. There is nothing unusual in 

 the formation of the first four parts, the femur and tibia usually 

 being quite long and somewhat cylindrical. The tarsus is the most 

 peculiar structure on the leg, and may be either simple or of two 

 segments, and usually ends in one or two claws. In the family 

 Thripidae, they belong to the former type. The remarkable bladder- 

 like structure, which for many years gave the name Physopoda to 

 this order, is protrusile from the end of the last tarsal segment. It 

 is present in both adults and larvae. The end of the tarsus is cup- 

 shaped, and into this cup the delicate membranous bladder is 

 attached. When the foot is at rest the bladder is invisible and is 

 withdrawn into the end segment. The bladder is protruded and 

 brought into action when the adult is resting on some surface or 

 walking around. The mechanism of the bladder has been partially 

 worked out by Jordon and Uzel, but as it is someAvhat intricate it 

 will not be described here. If a swollen bladder is pricked or rup- 

 tured, the blood pours out and the bladder collapses quickly. The 



